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 TARDIS lands on Argentia, a luxury space station temporally displaced sixty minutes outside of time to avoid tax, for the Doctor to collect diothanine crystals to make a new sonic screwdriver. Without the necessary papers, Superintendent Galgo takes the four travellers' DNA for a bioscan and directs them to the funeral of Carlo Mazzini, executive officer of the Mazzini Mining Company. They meet his family of demi-clones: his son Angelo, brother Francesco, sister Maria and nephews Joe, Peter and Paul.

Sofia Cozzi, the executor of Carlo's estate, reads out the will bequeathing everything, including 9,000,000,000 credits, to Angelo. The Doctor and Adric follow him to the sync pods to collect diothanine crystals, although all but one have seemingly been wiped out by a temporal anomaly, and Adric sees Angelo killed by somebody in a silver mask and a black hat with an incineration beam. Galgo puts Argentia under lockdown after confirming that the ash in the pod belongs to him and Joe points out to Tegan that Francesco, the next in line, was not with everyone else during the murder. However, Francesco has been killed by the bite of a reptilian arthropod.

Part two
The Doctor and Galgo kill the reptile and save Tegan, but it sprays Galgo with its nerve toxin and he requires medical attention. Dissecting the reptile, the Doctor is unable to identify its species and sends Nyssa to the TARDIS to investigate whilst he and Adric examine Carlo's villa where Angelo was staying. The Doctor suspects that the inheritance might not be the sole prize of the killer upon finding that a painting that Angelo saved from 1944 has been stolen and sends Adric to help Nyssa before visiting Galgo.

Joe tells Tegan that Maria, the next in line, is unlikely to be the killer but her cosmetics company on Suganda is rumoured to be nearing bankruptcy. Nyssa identifies the reptile as a Sugandian Normic and the Doctor goes to see Maria, who accuses Sofia of being behind the killings and professes her own innocence. Being between marriages, she attempts to seduce him and dies suddenly. Galgo examines the crime scene and detects the fast-acting poison hydroxatine in Maria's system and arrests the Doctor on suspicion of the three murders.

Part three
After visiting the Doctor in his neutron field cell, Adric finds a ventilation system in the villa which he suspects was used by whoever stole the painting, although Sofia is doubtful, and flees from discarded Baby Chuckles to a karaoke bar where he is joined by Galgo. They come across the corpse of Tom Rossi, Carlo's previous assistant. Nyssa joins them after discovering that a biomechanical drone injected Maria with the hydroxatine and they go to search Paul and Peter's room at the Hotel Excelsior, finding Paul dead and heading into the ventilation system to locate Peter.

Tegan, now suspicious of Joe, updates the Doctor on the investigations and goes to inform the others when he deduces that the murderer is using knowledge gained by time travel. Meanwhile, the group corner Peter, who claims that he killed Paul by accident whilst fighting over the painting but denies having stolen it or being behind the murders. Before he can elaborate further on the painting, he is killed by a figure with a cryo-blaster and the group run after the killer. They trap the killer above the oxygen gardens and Tegan and Sofia arrive, but Sofia draws a gun and reveals that she has been working with the killer. They overload the turbine and the group hold on to stop themselves being sucked in.

Part four
Having convinced the guardbot Bernard that it was impossible for him to have been the murderer, the Doctor saves the group in the TARDIS. Tegan finds Joe tied up in the villa as part of a trap and is captured, but they are saved with the help of an army of Baby Chuckles and the Doctor unmasks the killer as Angelo. Angelo confesses that he visited the future and saw that Peter and Paul ended up with his father's fortune after the rest of the family killed one another, leading him to come back to kill his family and use the painting to frame them.

Sofia beams Angelo and Adric, now a hostage, to their timeship to get away through a wormhole created by a quantum tear which will leave Argentia completely cut off from the rest of the universe and protect Angelo from the paradox of him having killed his earlier self to hide himself from the bioscan. The Doctor uses his diothanine crystal to focus the energy of the field generator and seal the tear, but Angelo tries to leave despite his and Adric's warnings and he turns to ash because of the paradox. Galgo arrests Sofia and Tegan declines Joe's offer of staying on Argentia or returning to Heathrow with him, telling him that her friends need her.

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 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 travelling 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 travelling 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)
 * Nicky Newman's Intergalactic Song Contest entry song is heard in the Karaoke bar Adric and Galga fall into. (AUDIO: Bang-Bang-a-Boom!)
 * Maclintock's Candy Burgers (TV: The Beast Below) and Henrik's Department Store (TV: Rose) are mentioned by Zaleb 5.