The Selachian Gambit was the eighth story of the sixth series in The Companion Chronicles. It was produced by Big Finish Productions. It was written by Steve Lyons and featured Jamie McCrimmon and Polly Wright.
Ben, Polly, Jamie and the Doctor prepare to leave the Galacti-bank when they find the TARDIS clamped by a yellow obstruction, preventing them from getting inside to take off. They head inside the bank, as the Doctor suspects that by opening an account they can use that to pay the fee and have the clamp removed. Just then the bank is invaded by the Selachians, who attempt to break into and rob the bank's vaults. They discover that the vault is dimensionally transcendental to protect the things inside and Tompkins, the bank manager, does not have the key as it continually changes so they create a hostage situation, demanding they be given access to the vault as commander Scalon arrives to deal with the situation. After the Selachians murder the first hostage, the Doctor offers them a deal: he'll help them break into the vault and negotiate a hostage deal with Scanlon if they don't hurt anyone else. They agree.
Polly meanwhile is permitted to go to the kitchen to prepare tea for everyone during the tense negotiations and discovers Ben having hid himself in the wall earlier when the Selachians broke in. The make a plan and create glue bombs to try attack the Selachians with and Polly brings out the tea but secretly tells Jamie their plan (while the Doctor is too busy with the negotiations) and gives him a glue bomb. However, she is released along with a few other bank patrons as per the Doctor's orders to keep her safe. Jamie, thinking he's been signaled by Ben, attacks the Selachians but fails. Ben comes out to defend him but in the ensuing scuffle, Ben reveals that a bomb has been planted in the wall, thinking it is a Selachian ploy but it turns out not to have been put there by the Selachians...
The Doctor attempts to analyze the bomb but accidentally activates it. Meanwhile Polly and the other released hostages are taken aboard Scalon's ship where she realises Scalon plans to take the bank back by force by any means necessary. Meanwhile Jamie manages to deactivate the bomb using the glue bomb to stop the timer. The Selachians, however, manage to break into the vault. Polly, onboard Scalon's ship, realises that the Selachians aren't after money, coming to the conclusion after realising that the parking clamp on the TARDIS wouldn't accept regular money, nor is that stored in the vaults. Scalon confirms her thoughts and one of the bank's largest clients are weapons manufacturers who store their plans and weapons in the vaults, which the Selachians have come to steal. The Selachians discover, however, that there is nothing in the vaults and that they had been robbed previously. It is revealed unwillingly by Tompkin that the bank is lying about its state and is not doing well, hence they robbed their own stores, lured the Selachians into a trap, tipped off Scalon to their presence so they would take the fall and collect on the insurance. The Selachains are enraged by this revelation and reactivate the bomb using their own timer and take two hostages, Ben and Jamie, at the Doctor's behest to keep them safe.
Once outside though, Jamie and Ben trick the Selachians and escape with the help of the last glue bomb and go back to warn the Doctor of the Selachian's plans to detonate the bomb anyway after their escape despite them promising not to in exchange for the hostages originally. However, Scalon's ship fires and destroys the Selachian ship as it attempts to escape but the bomb detonates and supposedly destroys the bank as Polly watches in horror at the unfolding events aboard Scalon's ship.
However, the Doctor manages to save everyone using the vault's dimensionally transcendental abilities and materialises them aboard Scalon's ship. Tompkins, in a change of heart, offers the clients and bank patrons free reimbursement and a handsome reward for the Doctor and company for saving them all.
Ben, Jamie and Polly wait by the TARDIS and the Doctor soon finds them while Ben excitedly exclaims that they've been offered very large compensation and is eagerly awaiting his credits. His hopes are dashed though when the Doctor explains to them all that he directed Tompkins to give the money to charity but asked a small amount be set aside, then pulls out the card and says an amount just large enough to pay the fee to remove the parking clamp.
- The Galacti-Bank vault utilises dimensional transcendentalism. The contents of the vault are contained in a pocket universe which can only be accessed by using the correct combination, which changes four times per day.
- The security for the Galacti-Bank Corporation is supplied by Tartarus Security.
- Selachians have an embassy on Pluto.
- The TARDIS is clamped with a force field around it preventing the travellers access to it until a 10 credit fee is paid.
- Ben and Polly make "glue bombs" from glue that Ben finds in a ventilation shaft used to secure the bank's structure from space-based strikes.
- Polly makes everyone tea.
- Selachians are aquatic; their suits contain water but the water needs to be oxygenated, which is done through a vent near the fin on the suits.
- Polly describes the particular branch of the Galacti-bank as "the shape of a spinning top floating against the backdrop of a thousand stars".
- Lady Sylvia mentions transmats.
- The Selachians call Jamie a skirt-wearing human; Jamie wears a kilt.
- The Doctor claims he needs to access dimensional stabilizers to return the vault that saves them to proper time.
- The G-bomb is a device that can collapse a planet into a black hole within seconds. The blueprints for such a device were locked in the vaults of the bank at some point before the robbery.
- This audio drama was recorded on 21 October 2011 at The Moat Studios.
- It was released on 10 February 2012.
- For the benefit of listeners without knowledge of the BBC Past Doctor Adventures, no direct references are made to The Murder Game, the novel in which the Doctor, Ben and Polly first encountered the Selachians. Any necessary information about the Selachians is delivered to the audience through Jamie, who has not met them before.
- This story was known as "The Vault" but changed due to Tales from the Vault being commissioned.
- This story was told from Jamie's perspective, with Polly providing additional dialogue.
- Jamie refers to the Battle of Culloden. (TV: The Highlanders)
- The Doctor, Ben and Polly previously encountered the Selachians aboard the Hotel Galaxian spacecraft in 2136 (PROSE: The Murder Game) whereas the Doctor, Jamie and Zoe Heriot would later do so on Ockora and Kalaya in 2204 (PROSE: The Final Sanction). Many years later in his personal timeline, the Seventh Doctor encountered them on the Moonbase in 2044 in an alternative timeline. (AUDIO: The Architects of History)
- Jamie and Ben refer to their escape from the Milice in Vichy France in February 1944. (AUDIO: Resistance)
- The Doctor claims that the forms to apply for a bank account are impossible to fill out, as they require a name and an address (which he supposedly doesn't have). (TV: An Unearthly Child et al.)
- Polly is surprised when the Doctor accepts opening an account with the bank to store his money/credits because the Doctor usually never carries money. (TV: The End of the World, The Runaway Bride et al.) The Doctor did provide money for his/her companions on rare occasions. (TV: Remembrance of the Daleks et al.)