Silver Nemesis (TV story)

Silver Nemesis was the third story of Season 25 of Doctor Who, and the twenty-fifth anniversary special.

To commemorate this, John Nathan-Turner chose silver as a theme for the story. Kevin Clarke contacted Andrew Cartmel and asked if he could write a script for the series. The only slot left was the special and Clarke claimed to have the perfect script. In fact, he didn't, but when he met with Nathan-Turner, he proposed to ask the question: who is the Doctor?

Another theme Nathan-Turner wanted was royalty, and so Windsor Castle was introduced. He even sent a letter to, asking him if he wanted to appear. He declined, but JNT took it to be that he had wanted to appear, but had stopped him doing so. In the press, stories circulated that he would be making an appearance and the palace was forced to release a statement denying it.

Arundel Castle doubled for Windsor, and several figures from the history of Doctor Who turned out to play tourists, including Vere Lorimer, Nicholas Courtney, Fiona Cumming, Peter Moffatt and Kevin Clarke himself.

Synopsis
Earth, 1988: While the Seventh Doctor and Ace flee from emotionless men wielding futuristic pistols, Herr de Flores is intent on heralding the Fourth Reich. Meanwhile, the villainous Lady Peinforte uses black magic to propel herself forward from 1638 for a final confrontation with her sworn enemy — the Doctor.

As the Doctor desperately evades multiple enemies, a meteor containing a Gallifreyan super-weapon is hurtling towards the planet. Whoever controls the statue will hold the power of life and death over the entire universe...

Part one
South America, 22 November 1988: In an office full of Nazi imagery, a man looks at a computer screen displaying details on which he sees "Landing Location, Windsor, Grid Ref: 74W 32N, November 23, 1988". Outside, his superior, de Flores, is about to shoot a parrot with a bow and arrow when the man informs him about the news.

Windsor, England, 1638: A finely dressed woman is shooting pigeons with a bow and arrow whilst her servant looks on. In her house, an elderly mathematician is performing complex calculations. The woman enters and demands to know how long his work will take, but he is too engrossed in his work to answer her. She goes to the fireplace and, picking up a poisoned arrow, hands it to her servant and tells him to put it with the others. He enquires after a silver arrow, and she replies that she will deal with that arrow personally.

Back in the Nazi office, de Flores addresses a group of followers, telling them they are at the turning point of history. He proposes a toast to the fourth Reich, before taking a silver bow from a display case, preparing to board an aircraft. In space, a comet is seen from which a glowing energy emanates…

Back in Windsor, the mathematician finally reveals the result of his calculations to the woman, telling her that the Nemesis comet circles the earth every 25 years, and its decaying trajectory means that it will eventually fall to Earth from the point where it originally departed — the meadow outside. This will occur on 23 November 1988.

At a jazz performance by Courtney Pine, the Seventh Doctor and Ace relax and enjoy the music. Ace's newspaper — namely the Daily Mirror — has a story about a comet heading to Earth, but she is more interested in the football results. The Doctor hears a bleeping from his pocket watch, and wonders of what it is trying to remind him. Pine's performance ends to applause and Ace asks him to sign a tape for her.

As they head back to the TARDIS, a concealed marksman raises a gun towards them. At the sound of gunfire, Ace and the Doctor duck down and retreat quickly towards the TARDIS, but have to jump in the river to escape their pursuers. Two men arrive wielding guns and wearing headsets, but, assuming they must have got their targets, they leave again. The Doctor and Ace then struggle back on to the riverbank, safe now.

In 1638, the mathematician dreams of great inventions that he could discover. The lady tells her servant to bring forth the potion, and he replies that they only require the final ingredient, human blood. They look meaningfully towards the mathematician…

The Doctor fetches out a new tape deck that he has built to replace the one of Ace's that had been destroyed by the Daleks. This one, however, can do much more than play tapes. The Doctor tells Ace that his reminder had a terminal rating, meaning some planet somewhere is facing imminent destruction, and an image of the planet Earth appears on the tape deck…

In 1638, the woman and her servant drink their magic potion and are surrounded by a glowing miasma. They begin to travel forwards through time. They appear in present day Windsor in the middle of a crowded cafe.

The Doctor admits that he has known about the possible destruction of Earth for 350 years. He and Ace take a quick trip in the TARDIS to Windsor Castle. In its basement, the Doctor tells Ace he is looking for a silver bow.

As the comet finally hits Earth, the woman's arrow begins to pulsate with light. In the castle, the Doctor and Ace feel the force of the impact. The Doctor tells Ace that it is the return to Earth of a comet called Nemesis, and then reveals that it was he who had launched it into space in the first place. Led by their glowing bow, the group of Nazis heads towards the comet in a van.

De Flores is in no rush to retrieve the Nemesis yet, as the comet will be too hot due to its descent through the atmosphere. He tells his soldiers they will wait in a hotel leaving British police to guard the site, unaware of the true power of the Nemesis. In the castle, Ace finds a card telling the history of the bow, relating how it disappeared in 1788, and that unless a place is kept in the castle for its return, the entire silver statue will return to destroy the world. The Doctor tells her that the statue has indeed returned with that purpose. At this point, the lights dim, and Ace thinks it is a power cut.

Travelling back in time to 1638, the Doctor and Ace go to the time travelling woman's house in Windsor. Seeing the corpse of the mathematician, the Doctor hurriedly covers it with a cloth so that Ace does not see it. The Doctor sees the mathematician's calculations and is impressed that he had been able to work out when the Nemesis comet will return to Earth, only months since the Doctor's previous visit.

The Doctor reveals that the woman — Lady Peinforte — made the Nemesis statue, depicting herself, out of a silver metal that fell to Earth in the meadow outside her house. The Doctor sees a chessboard, and notes that the game is going rather badly. He tells Ace that Peinforte managed to travel forward in time to 1988 using the arrow and a rudimentary knowledge of time travel, but mostly black magic. He says that she has a nose for secrets. The Doctor tells Ace the statue is made of a living metal — validium — which is capable of great destruction.

Peinforte and her servant Richard withdraw from the statue to assess the strength of the police guarding it. The police are having their own problems. Their radios are not working — the batteries are dead. Around the comet crash site, vents emerge from the ground spewing gas, causing the policemen to choke and fall unconscious.

The TARDIS materialises outside Windsor Castle in 1988. The Doctor and Ace follow a group of tourists on a guided tour. Seeing a no entry sign, they sneak into the castle. Hearing the bark of dogs, they see a woman coming towards them with several corgis. Although the Doctor does not recognise the woman, Ace immediately realises that it is the Queen Elizabeth II and drags him into hiding. However, when she tells him who it was, he races after the Queen, saying they need the armed forces and police on their side, and what better person could they ask? The Doctor and Ace are seized by security guards before they can get anywhere near the Queen.

The Doctor informs the guards that they got into the castle by travelling in time and space, but they are incredulous. The Doctor tells them the fate of every living person is in danger, but the guards do not believe him. The Doctor dons a pair of oversized glasses and glaring at them intones, "You will believe me! You will let us go!" Distracted by this spectacle, the Doctor and Ace flee into the corridors of the castle. As they run, Ace sees a portrait of herself hanging on a stairwell wall. When she says she does not remember this happening, the Doctor tells her that it has not happened yet.

Richard asks Peinforte what she will do when she gains control of the Nemesis, and she replies that first she will exact revenge on that "predictable little man". She predicts that he will soon arrive, and tells Richard she knows the secret of the "nameless Doctor."

De Flores and his Nazis make their move for the Nemesis comet and see the unconscious policemen. He takes the bow case and places it on the comet, and within the Nemesis statue begins to glow. The Doctor and Ace arrive, and De Flores demands they hand over the arrow. The Doctor reveals that the bow and arrow give the validium metal critical mass. The Doctor confronts De Flores and asks if he has observed the advanced technology, which has been used to attack the policemen, and the power blackouts that have been occurring over the last few days. De Flores threatens to shoot Ace if they do not tell him where the arrow is, but at this moment a large spacecraft lands near the crash site. The doors open and from within emerge a troop of Cybermen…

Part two
The Cyber-Leader recognises the Doctor, even though his appearance has changed, and tells the onlookers that the Cybermen had predicted his presence. The Nazis open fire on the Cybermen but their bullets are ineffective. The Cybermen open fire and drive the Nazis away. The Doctor says that this happened before, but before it was the Roundheads and Lady Peinforte. Peinforte shoots one of the Cybermen with a bow and arrow and de Flores finds the arrows to be gold-tipped.

Peinforte and Richard withdraw, allowing the Nazis and the Cybermen to fight it out, hoping to retrieve the Nemesis in the aftermath. In the confusion, the Doctor and Ace manage to seize the silver bow and return to the TARDIS. Peinforte sees this and tries to shoot them, but her arrow thuds into the TARDIS door just as it dematerialises.

While Peinforte and Richard enter the town of Windsor, the Cybermen begin to cut the Nemesis statue free of the comet. The Doctor and Ace go back to Peinforte's house in 1638. The body of the mathematician has gone, and the chess pieces have also been moved. The Doctor tells Ace that although the mathematician was a genius, he had needed a little help to get started. The Doctor picks up a piece of paper from the desk and throws it into the fireplace. The Doctor makes a further move on the chessboard, and they leave.

Materialising back in the present day, the Doctor explains that validium was created on ancient Gallifrey by Omega and Rassilon as the ultimate defence. Some of it, however, left Gallifrey, and now they must stop Peinforte or anyone else reuniting the statue, the bow and the arrow. Using the bow to lead them, they proceed in the direction of the statue.

In Windsor, Peinforte and Richard are confronted by two thugs, who think they are mugging social workers. The Doctor finds and questions them later; they had been left semi-naked, dangling from a tree.

As Richard is terrified by the sight of a bizarre creature, a llama, Peinforte tells him that if he does not help her retrieve the Nemesis, she will abandon him in this future time. He then sees that they are standing by a memorial statue. She tells him that it is his tomb, placed in the grounds of her own burial place. The arrow starts glowing and they realise that that is where the Cybermen have taken the Nemesis statue. As they scour the tomb for Nemesis, the Cybermen prepare to attack, but realising they are armed with gold arrows retreat. Opening up her grave, they see that it does not contain her bones.

Ace destroys the Cybermen vehicle with Nitro-9 explosive. De Flores strikes a deal with the Cyber-Leader to kill Peinforte and Richard in exchange for a share of control of Earth after its conquest. The Cybermen have no intention of honouring the deal, and plan to kill the Nazis after the death of Peinforte.

The Doctor tells Ace that every time the Nemesis comet approached Earth in its 25 year orbit, it caused destruction: in 1913, the eve of the First World War; 1938, Hitler annexed Austria; 1963 Kennedy assassinated, and now it is 1988. They use the tape deck scanner to try to find the Cyber-fleet.

Opening up the grave fully, Peinforte gazes upon her own image shown on the Nemesis statue. However, De Flores and his man arrives with guns, and Richard has only one arrow left. In fear, he hands over the arrow to De Flores and drags Peinforte away, leaving the Nazis in control of Nemesis. De Flores believes he now has all three parts of the validium. He places the arrow in the statue's hands, and it becomes more animated. The Cybermen arrive and ask De Flores where the bow is. When he opens the case he sees that he does not have it at all.

The Doctor sees a lizard emerge from hiding and realises the Cyber-fleet is shrouded. He makes an adjustment to the tape deck and reveals the entire fleet of Cyber-warships, thousands of them…

Part three
The Doctor decides to activate the validium by taking the bow to the crypt. When Ace seems frightened, the Doctor tells her she can wait in the TARDIS, but she refuses and wants to accompany the Doctor.

Meanwhile, De Flores realises he has overplayed his hand and tries to negotiate with the Cyber-Leader. The Cyber-Leader orders his lieutenant to kill De Flores, but he throws gold dust in the Leader's face and flees.

As the Doctor and Ace arrive at the crypt, the jazz tape finishes playing and the Cybermen's communications begin working. The Doctor enters the crypt holding the bow, and, manoeuvring past the Cybermen with Ace, places the bow in the statue's hands but snatches it away again. The statue awakens and begins to follow the bow.

Going back to 1638, the Doctor continues his chess game against his unknown opponent. Ace asks him who brought the validium to Earth in the first place, and what is really going on, but he remains silent. Taking a bag of gold coins, they leave.

Peinforte begins to rant about all power being hers and her intent to retrieve the Nemesis. They come to the road and attempt to hitch a lift in a passing car. Richard stands with his thumb out, but no cars stop for them. Seeing this fail, Peinforte steps into the middle of the road. A large car stops, and an American woman offers to take them into Windsor. She tells them that she is in England discovering her roots. Revealing she is descended from the 17th century Remington family, Peinforte calls them thieves and swindlers. Mentioning a Dorothea Remington, the American woman recognises the name, and Peinforte knows that Dorothea died in 1621 from a slow poison.

Meanwhile, the Doctor and Ace materialise inside the hangar containing the comet. Soon the Nemesis statue arrives, and the Doctor gives it the bow. The Nemesis speaks to Ace, telling her that it was fashioned by Peinforte into its current beautiful form, but that it has also had horrific forms in the past, and will again in the future. The Cybermen arrive and Ace shoots one down using a gold coin and shoots it with a slingshot.

The Cybermen pursue her, but she manages to elude them. The Doctor sets the trajectory of the rocket sled containing the Nemesis, headed for the Cyber-fleet. Ace becomes trapped on a gantry between two Cybermen and the Cyber-Leader, with only a single remaining gold coin. The Cybermen lift their guns to shoot her, but she fires the gold coin at the Cyber-Leader and ducks, causing the other two Cybermen to shoot each other instead. The Nemesis asks the Doctor if she must destroy the entire Cyber-fleet, to which he says that she must. She asks the Doctor whether she will be needed again, or whether she will have her freedom, but the Doctor hushes her.

Ace arrives down from the gantry, but is surrounded by two more Cybermen. They demand that the Doctor hands the bow over to them, but the Doctor threatens to destroy the bow if they harm her. Placing it in front of the rocket sled engines, he grabs Ace. As the two Cybermen advance towards them, the engines fire, killing the two Cybermen. However, up on the gantry the Cyber-Leader plucks the gold coin from its chest unit.

De Flores arrives and picks up the bow. He speaks to the Nemesis, but she remains silent. The Cyber-Leader raises his gun and shoots De Flores dead, and demands that the Doctor hands over the bow. At this point, Peinforte and Richard arrive. Demanding the bow for herself, she asks Ace who the Doctor is, and whether she knows where he came from. Ace says that nobody knows who the Doctor is, but Peinforte says that she does. When Ace asks how, she says the Nemesis told her.

The Doctor asks what will happen if he gives her the bow, to which Peinforte replies his power will be hers, but his secrets remain his own. Appearing to concede defeat, the Doctor says he is surrendering, but not to Peinforte, rather to the Cybermen. Peinforte threatens to reveal his secrets, so he calls her bluff. She says that she will tell them of Gallifrey, of the Old Time, the time of Chaos. However, the Cyber-Leader says that the secrets of the Time Lords are of no interest of the Cybermen.

The Cyber-Leader tells the Doctor to cancel the Nemesis's destructive capabilities. The Doctor asks the statue if she understands the Cyber-Leader's instructions, and she replies, "Perfectly".

The triumphant Cyber-Leader tells the Doctor to set the statue's course to rendezvous with the Cyber-fleet. He tells them that the Earth will become their new base planet, the new Mondas. As the Nemesis launches, Peinforte screams and throws herself into the rocket sled and merges with the Nemesis.

The rocket sled takes off and heads out into space. It arrives in the midst of the Cyber-fleet and there is an enormous explosion, destroying all of the Cyber-warships. The Cyber-Leader asks how it is possible, and the Doctor replies that he merely asked if Nemesis had understood the instruction, but had not said anything about obeying them. The Cyber-Leader prepares to kill the Doctor, but Richard grabs the gold-tipped arrow from the TARDIS door and stabs it into the Cyber-Leader's chest unit, finally killing it.

The Doctor and Ace return Richard to 1638. There, Richard and a Stuart woman perform a concert for them. Ace asks the Doctor who he really is, but he just puts a finger to his lips and listens to the music…

Cast

 * The Doctor - Sylvester McCoy
 * Ace - Sophie Aldred
 * De Flores - Anton Diffring
 * Karl - Metin Yenal
 * Lady Peinforte - Fiona Walker
 * Richard Maynarde - Gerard Murphy
 * Mathematician - Leslie French
 * Security Guard - Martyn Read
 * Mrs Remington - Dolores Gray
 * Himself - Courtney Pine
 * Cyber-Leader - David Banks
 * Cyber-Lieutenant - Mark Hardy
 * Cyberman - Brian Orrell
 * Skinheads - Chris Chering, Symond Lawes
 * Jazz Quartet - Adrian Read, Ernest Mothle, Frank Tontoh

Crew

 * Writer - Kevin Clarke
 * Assistant Floor Managers - Lynn Grant, Jeremy Fry
 * Costumes - Richard Croft
 * Designer - John Asbridge
 * Incidental Music - Keff McCulloch
 * Make-Up - Dorka Nieradzik
 * OB Cameramen - Barry Chaston, Alan Jessop
 * Producer - John Nathan-Turner
 * Production Assistant - Jane Wellesley
 * Production Associate - June Collins
 * Script Editor - Andrew Cartmel
 * Special Sounds - Dick Mills
 * Stunt Arrangers - Paul Heasman, Nick Gillard
 * Theme Arrangement - Keff McCulloch
 * Title Music - Ron Grainer
 * Visual Effects - Perry Brahan

The Doctor

 * The Doctor indicates that he knows Queen Elizabeth II.
 * The Doctor's pocket watch warns him of the imminence of certain dangerous moments.

Individuals

 * Ace reads about Charlton Athletic in the Daily Mirror.

Gallifrey

 * From Nemesis Lady Peinforte learned of a grim secret of the Doctor's from the "Old Time, the Time of Chaos".
 * Validium is a Gallifreyan living metal. Peinforte calls the validium her Nemesis.

Minerals

 * Ace uses gold to fight the Cybermen, and Lady Peinforte's arrows are made of gold.

Story notes

 * This story had working titles of The Harbinger and Nemesis.
 * Nicholas Courtney is present in the large crowd scene in the palace.
 * This story marked the 25th anniversary of Doctor Who, giving the "Silver" in the title a double meaning.
 * The setting is on November 23 - another anniversary reference, being the date of the airing of the first episode in 1963.
 * Courtney Pine guest stars as himself in Part One.
 * The Doctor's new stereo (for Ace) was to have Zygon like speakers, but these were replaced with more conventional technological ones.
 * The gasworks site (the site of the warehouse and main battle sequence) takes place on the site which would become the site for the Millennium Dome.
 * An outtake from this episode sees Sylvester McCoy tripping over a bush and then trying to stab it with his umbrella. The blooper appears in a contemporary PBS documentary on the making of the serial, and was also played during McCoy's 1988 "Clown Court" appearance on The Noel Edmunds Saturday Roadshow. This was later included on the 2009 DVD release of TV: Delta and the Bannermen.
 * It was originally scripted for the policemen at the Nemesis' crash site to be killed by a swarm of Cybermats.
 * Prince Edward was asked to appear in this story by John Nathan-Turner, but the royal family wrote a letter in response declaring that it would be inappropriate for this appearance to happen. (DOC: Industrial Action)
 * This story marks the only on-screen appearance of Mark VII Cybermen.
 * In DOC: Industrial Action, Kevin Clarke explains that the question "Doctor Who?" was the original basis of the story.
 * This is the last episode to feature Cybermen before Doctor Who's cancellation in 1989.

Ratings

 * Part 1 - 6.1 million viewers
 * Part 2 - 5.2 million viewers
 * Part 3 - 5.2 million viewers

Myths and rumours

 * John Nathan-Turner attempted to get the real Queen Elizabeth II to appear as herself in the serial (much as members of the Royal Family had appeared on an episode of Coronation Street). This could not be arranged, so an impersonator was enlisted.

Filming locations

 * Greenwich Gas Works, Tunnel Avenue, North Greenwich (where the Nemesis lands)
 * Arundel Castle, Arundel, West Sussex (stand in for Windsor Castle)
 * London Road, Arundel, West Sussex (one of the roads Peinforte and Richard walk down)
 * Casa Del Mar, Aldsworth Avenue, Goring-by-Sea, West Sussex (De Flores' house)
 * Arundel Estate (now known as Arundel Park), Arundel, West Sussex
 * High Street / Tarrant Street, Arundel, West Sussex
 * St Mary's House, The Street, Bramber, West Sussex (exterior of Peinforte's house)
 * Black Jack's Mill, Harefield, Middlesex (location where Ace and the Doctor are listening to music)

Production errors

 * The story is set in November, but the Courtney Pine Quartet are playing outside in the sunshine, and Ace is in a T-shirt. The foliage is decidedly lush, green, and non-Autumnal as well.
 * The camera operator stumbles or knocks into something when following Ace across the gantry in the third episode.
 * In episode two a helicopter was used to simulate the Cybership landing, the craft being superimposed over it. However, the blades are sometimes visible.

Continuity

 * Ace compares the events she encounters here with TV: Remembrance of the Daleks. Ace also mentions that her stereo was destroyed by the Daleks (which occurred in the same story).
 * A Cyberman head appears in TV: Dalek.
 * Alternate universe Cybermen were introduced in TV: Rise of the Cybermen.
 * Cybermen of Mondasian origins were seen again in TV: Closing Time
 * Lady Peinforte shows her servant, Richard Maynarde, his grave. In TV: Revelation of the Daleks, the Sixth Doctor explains to Peri that if he took her to Earth after she had died, she could see her own gravestone.
 * The Doctor will later visit his own tomb. (TV: The Name of the Doctor)


 * The Doctor plays chess against an unknown opponent, thought to be Fenric. The Doctor battles Fenric later on in TV: The Curse of Fenric. Before this, in the story Battlefield, Morgaine speaks of always beating the Doctor at chess. Morgaine, like Fenric, is a powerful being from another dimension.
 * Battlefield also deals with Time as a major factor. Lady Peinforte's tomb does not contain her bones because she is destroyed in space when the Nemesis explodes. In Battlefield, the events occur because of what the Doctor will do in the future, leading to the Doctor writing himself a note and claiming that he should have given himself more warning.


 * Based solely on this episode, it should be impossible for anyone from 1638 to calculate correctly a day 350 years later as in 1752 the Julian calendar was 'brought into line' with the Gregorian one (effectively meaning that 11 days from 3 to 13 September were skipped over). However, this seeming discrepancy is later explained in The Curse of Fenric. As viewers later discover, this is not an error, but further proof that Fenric has consistently been manipulating the timeline in order to control Ace.
 * At about 6 minutes into episode two, back in Lady Peinforte's home, the Doctor retrieves a note and burns it. He tells Ace that although the mathematician was a genius, he did need a nudge in the right direction.
 * In PROSE: Interference - Book Two there is another validium-based weapon featured.
 * Early in Part Two the Doctor dematerialises the TARDIS as an arrow hits it. The same thing happens again at the end of TV: The Shakespeare Code. In both cases the arrow dematerialises with the TARDIS.
 * The extended edition features a painting of Ace in early French clothing. This is explained in PROSE: Set Piece.
 * Queen Elizabeth II would appear again years later in Voyage of the Damned (with an indirect reference to her made in The Christmas Invasion).
 * The Doctor wears a fez and briefly carries a mop about 12 minutes into part 1. The Eleventh Doctor would later wear a fez and carry a mop in TV: The Big Bang.
 * Lady Peinforte, either purposefully or unwittingly, asks "the First Question" in her final confrontation with the Doctor in part 3. She threatens, "Doctor Who? Have you never wondered where he came from?" "Doctor Who?" would again be used as a threat. (TV: The Wedding of River Song, The Name of the Doctor)
 * The Doctor dons a pair of "brainy specs", akin to the Fifth Doctor. However, he uses them to hypnotise two guards in a manner similar to the glasses utilised by the War Lords. (TV: The War Games)

DVD releases

 * This story was first released on DVD in the UK on 9 August 2010 as part of the Cybermen boxset. The one disc set includes a restored version of the story, as well as the following special features:
 * Commentary by Sylvester McCoy (The Doctor), Sophie Aldred (Ace), Chris Clough (Director) and Andrew Cartmel (Script Editor).
 * Industrial Action
 * Deleted And Extended Scenes
 * Trailers And Continuity
 * Coming Soon Trailer
 * Radio Times Billings
 * Production Subtitles
 * Photo Gallery


 * Bbcdvd-cybermenboxset.jpg DVD contains the original three part broadcast version, much to the consternation of a number of Doctor Who fans who consider the extended version to be the definitive one. It does however contain 22 minutes' worth of deleted scenes. While including some never before seen, it nevertheless omits two scenes and several instances of cut dialogue, now only to be found in the previous VHS release.

VHS releases
A VHS edition of Silver Nemesis was released by BBC Video in 1993. This was an "extended edition" containing scenes not included in the original broadcast.