Serpent in the Silver Mask (audio story)

Serpent in the Silver Mask was the two hundred and thirty-sixth story in Big Finish's monthly range. It was written by David Llewellyn and featured Peter Davison as the Fifth Doctor, Matthew Waterhouse as Adric, Sarah Sutton as Nyssa and Janet Fielding as Tegan Jovanka.

Publisher's summary
You are cordially invited to Argentia, the galaxy’s most exclusive tax haven, to attend the funeral of mining magnate Carlo Mazzini. The memorial service will be followed by music, light refreshments, and murder!

Carlo’s heirs have come to say their final goodbyes (and find out how much they’ve inherited) but when a masked killer begins picking them off one by one, Argentia goes into lock-down, closed off behind its own temporal displacement field.

Can the Doctor, Nyssa, Tegan and Adric apprehend the murderer before Argentia – and everyone on board - is forever cut off from the rest of the Universe?

Part one
The Doctor, Tegan, Nyssa and Adric arrive in the TARDIS on Argentia, with the Doctor on a mission to get diothanine crystals so he can make a new sonic screwdriver. They run into some trouble with a robot and Superintendent Galgo but after a quick DNA scan they are approved to attend the funeral currently being hosted for the deceased Carlo Mazzini, a wealthy billionaire industrialist who ran an interplanetary mining company called The Mighty Mazzinis and who was an inhabitant, having recently passed away. The four split up and converse with the guests, most of them his family who are eager to know how much they have been left in Carlo's will. The will is eventually read, and Carlo's entire estate is bequeathed to his son Angelo Mazzini, much to the shock of the other guests and especially to the rest of the Mazzini family, as his father and he were not too close. Angelo is then escorted to a sink pod to contact his accountant about the news to settle matters, and the Doctor secretly follows, explaining that they're likely to find the diothanine crystals nearby there as they are used for sink pods and brings Adric with him but makes Nyssa and Tegan stay behind so as not arouse the suspicion of Superintendent Galgo, who has been keeping an eye on them the whole time.

The Doctor and Adric find the entrance to the mine stores of the diothanine crystal and the Doctor goes in while Adric keeps watch. Adric, however, ends up seeing Angelo, while using the pod, murdered by an assailant wearing a silver mask and a black hat. They call Superintendent Galgo, who heavily suspects them, however, they find the ashes of Angelo, likely to have been killed by and the result of an incineration beam and confirmed by a DNA scan, and the whole of Argentia is put on temporal lock-down with no time-travel ship or device able to transport anyway away from the current zone. Tegan talks with Joe Mazzini, whom she met earlier, who says he thinks he knows who killed Angelo, given they were missing during the party after the will reading. They find the Doctor but before Joe can say the Doctor already guessed that he suspects Francesco Mazzini who is mysteriously absent. Joe simply reaffirms that was his guess. Meanwhile, Francesco, having discovered the death, contacts some people about a deal since he is now next in line for the inheritance but is killed by the assailant. The Doctor, Tegan and Galgo find his dead body, leaving Nyssa and Adric to walk around and eavesdrop. Just then, Tegan looks up to discover a sort of reptilian arthropod is directly above her, and the Doctor warns her to stay still...

Part two
The Doctor and Galgo manage to kill the creature, however, some of its nerve toxins get onto Galgo and he collapses, the Doctor saying he needs to be seen to by a medical professional. They dissect the creature that attacked inside the TARDIS but can't pin-point its species. The Doctor explains that with Galgo indisposed they'll be heading the investigation themselves and tells Nyssa to stay in the TARDIS and find the creature's species while he, Adric, Tegan and Joe continue the investigation. The Doctor and Adric are taken by Sofia Cozzi to visit the vault where Angelo stored his valuable painting he uncovered in 1944 instead of on his ship, which the Doctor becomes heavily interested in. Eventually, the Doctor tells Adric to join and help Nyssa in the TARDIS while Tegan discusses suspects with Joe.

Maria Mazzini comes under suspicion by each of the parties while the Doctor visits Galgo. They all convene and the Doctor assures Galgo they will deal with the investigation while he recovers. He then goes to see Maria Mazzini. The Doctor begins questioning her but she proclaims her innocence and attempts to seduce the Doctor, however, inexplicably, she ends up dying right in front of him. Upon consulting with Galgo, it seems she was dosed with hydroxatine, a fast-acting poison, and Galgo arrests the Doctor, suspecting he is the real master-mind, despite Adric warning him this would happen several times throughout their investigation...

Part three
The Doctor is put under arrest and imprisoned in a neutron field while Galgo continues his investigation, to find irrefutable proof that the Doctor was the murderer while Adric, Nyssa and Tegan visit him, having been allowed to go free as they were merely classified as stowaways and Galgo doesn't have time to deal with them currently. They promise the Doctor they'll try prove his innocence and get him out and he suggests they start by finding out what happened to the painting while Galgo tells them they're free to investigate even if it's pointless. Adric then splits off to investigate the possibility of a secret passage used by the assailant. Meanwhile Joe catches up with Tegan, who at first is cold to him but warms up when he dispels her suspicions. The Doctor, meanwhile, attempts to lay out their suspects to himself in his cell.

Adric and Sofia find a loose cover part of the ventilation system that looks like it had been removed previously, and Adric crawls through it despite Sofia's warnings and much to her annoyance. Nyssa and Joe visit the body of his aunt Maria in the moratorium, and discover a tiny bot a picometer in size that injected the poison into her. Adric, meanwhile, winds up in a Gammaras, a karaoke bar in the hotel Excelsior, while running from Baby Chuckles, and is soon joined by Galgo who has come to investigate as well. The two find the body of Tom Rosse, Carlo Mazzini's previous assistant before Sofia. Next they find one of the twins, Paul Mazzini, dead, and suspect that Peter has taken the painting and is making an escape, with Galgo able to track his scent. It seems he's attempting to get away through the vents and they follow. Meanwhile, Tegan visits the Doctor and reveals her suspicions of Joe, despite liking him and leaves to find the others. She then makes her way to the hotel Excelsior. Eventually, Peter is cornered but reveals the twins didn't do it, and the death with the blaster was an accident over a squabble for the painting, but he is then killed by a shot from a cryo-beam and Nyssa and Galgo chase after the new figure that killed Peter. They eventually corner the killer in the oxygen garden but Sofia arrives with Tegan, reveals she has been in on the plan and she and the killer escape after breaking the control systems, leaving Tegan, Nyssa, Adric and Galgo locked in, about to be sucked into the massive fan below...

Part four
Suddenly, the TARDIS arrives and the Doctor manages to rescue them, explaining that he managed to logically convince Bernard, the robot guarding his cell, that it was impossible for him to have committed the murder and Bernard released him. They explain to him that Sofia was an accomplice of the killer but the Doctor explains that due to his time sitting alone in the cell and working it out with Bernard listening, he managed to deduce that and has also figured out who the killer is. Tegan thinks it's Joe's but the Doctor's explains it can't be and she rushes off to warn him despite the Doctor warning her to come back. He then takes Nyssa and Galgo to the lower levels where the time ships are parked. Tegan learns from a service bot that Sofia is in the Mazzini's villa where Joe is headed and heads there himself while the Doctor, Nyssa, Adric and Galgo find a vehicle in the lower levels that shouldn't be there.

Tegan finds the villa deserted and follows the sound of strange music into the house, and finds Joe tied up and he reveals it was a trap for them both. The killer confronts Tegan and reveals its plan to use the two as hostages when suddenly a Baby Chuckles comes into the room. The killer blasts it to smithereens but more arrive and attack the killer for destroying one of them. Distracted, the killer gets captured and the Doctor, Nyssa, Adric and Galgo reveal themselves and explain they had used the dolls as a distraction. They take off the killer's mask and find out it's Angelo Mazzini. The Doctor explains that he checked the logs of Angelo's ship and found that Angelo had done something illegal and traveled along his own personal timestream ten years forward. Angelo explains that he wanted to see what would happen after inheriting such a massive amount of money and reveals that the family all end up murdering each other in an attempt to claim the inheritance leaving Paul and Peter unscathed and inheriting it and Angelo explains his disgust at such idiots possessing his father's wealth. When Adric asks about Angelo killing himself, the Doctor realises that this is to his advantage because once he was registered as deceased on Argentia's systems, he would no longer be tracked and registered and would be free to move about the station undetected. He had used the painting as a scapegoat to frame (pun is acknowledged in the story) his family as well. Adric asks about that creating a paradox but the Doctor realises that since Argentia is in lock-down it is in a separate time and so the paradox is being held at bay. Just then, Angelo takes Adric hostage and communicates with Sofia to beam them aboard their escape ship, and they are teleported away. The Doctor explains they need to get to the field generator quickly.

Adric asks how they'll escape and Sofia explains that they've engineered a wormhole and are currently attempting to align the temporal drives, while Angelo mentions how good Sofia is with this "stuff". The Doctor and crew arrive on the control deck and look for the field fabricator. The Doctor explains someone broke in and created a quantum tear, causing a wormhole that he explains after being sealed would cause Argentia to be completely cut off in time trapping everyone inside. Galgo thinks all hope is lost but the Doctor explains that they can use the diothanine crystal to seal the quantum tear, however, he laments that he should have realised earlier what was going on when he explored the mine and only found the one, explaining that the other crystals must've been disintegrated by the quantum tear. They manage to stop it but the Doctor explains that Angelo still has Adric and if he leaves Argentia the paradox will catch up with him. Galgo retorts he is fine with it killing him but the Doctor, claiming he is not judge, jury and executioner, believes Angelo should be tried on Argentia instead. They take off to find him.

The Doctor locates Angelo's ship and tries to get him to open up and they open a communication channel and the Doctor explains what he did, telling Angelo that if he leaves the station, the paradox will catch up with him and he will be disintegrated just as he did to himself earlier. Angelo believes the Doctor to be bluffing, but when he asks Sofia, she is distraught as she simply doesn't know. Adric tries to convince him that the Doctor is not someone who would lie about such a thing, but Angelo ignores him and takes a chance and tries to escape, only to end up disintegrated and Sofia in tears. The Doctor, Galgo, Nyssa and Tegan get aboard and Galgo places her under arrest.

In the aftermath Galgo apologises to the Doctor for accusing and locking him up which the Doctor brushes off, and Tegan sadly parts ways with Joe, despite his offer to stay with him as he has now inherited Carlo's fortune, saying that although tempted by his offer, she wants to spend more time with her friends.

Cast

 * The Doctor - Peter Davison
 * Adric - Matthew Waterhouse
 * Nyssa - Sarah Sutton
 * Tegan - Janet Fielding
 * The Mazzini Family - Samuel West
 * Superintendent Galgo / Zaleb 5 - Phil Cornwell
 * Sofia Cozzi - Sophie Winkleman

Continuity

 * Tegan mentions she was a stewardess. (TV: Logopolis et al.)
 * When Adric asks the Doctor why he doesn't just ask the proper channels of communication for a the diothanine crystal, the Doctor explains that that sort of thing usually results in a firm "no", just like "Can I play near the waterfall?", "Can I join the Time Lord Academy?" or "Can I borrow that TARDIS?" (TV: The Day of the Doctor et al., AUDIO: The Beginning, et al.)
 * When trying to open a door, the Doctor claims that now would be a good time to have the sonic screwdriver. (AUDIO: The Crimes of Thomas Brewster et al.)
 * Agatha Christie and her novels are known in places as far out as Argentia. The tenth Doctor and Donna Noble would later meet her themselves. (TV: The Unicorn and the Wasp)
 * The Doctor mentions to Maria Mazzini that he is a Time Lord. (TV: The War Games et al.)
 * Maria claims the Doctor has "powerful thighs" while attempting to seduce him and asks if he does a lot of running. Many people explain that there is a lot of running involved when it comes to traveling with the Doctor, as mentioned by, for example, Donna Noble. (TV: The Doctor's Daughter)
 * The Doctor, while talking to the robot guard Bernard in his neutron field prison cell, talks about how countless times the people under his care have "grown up" and "left the nest". He refers to the many companions who decided to stop traveling with him and go off on their own to start their lives, such as his granddaughter Susan, Vicki, Ben and Polly, Victoria, Jo Grant and many others. (TV: The Dalek Invasion of Earth, The Romans, The Faceless Ones, Fury from the Deep, The Green Death et al.)
 * The Doctor also mentions to the robot how he was once exiled to and stuck on Earth for a time and that the UNIT canteen was disgusting. (TV: The War Games, Spearhead from Space et al.)
 * Adric, while being confronted by the Baby Chuckles dolls says, "Sorry, must dash", something the Fifth Doctor would sometimes say. Angelo also uses this line later while escaping their interrogation. (TV: The Five Doctors et al.)
 * When Tegan and the Doctor discuss the possibility that Joe might be the culprit, they each, talking out loud, go off on their own tangents, only to snap back to attention when each yells at the other "Have you been listening to a word I said?". The third Doctor and Jo had a very similar exchange on her final days working for UNIT. (TV: The Green Death)
 * The Doctor, upon discovering Angelo's ashes, when he attempts to escape Argentia, says "Ashes to ashes, dust to dust". He later uses the same line after tormenting the renegade Dalek Supreme that ends up killing itself. (TV: Remembrance of the Daleks)