The Vault (The Scales of Injustice)

The Vault contained alien artefacts and other objects of interest taken by C19 from both before and after the formation of UNIT. (PROSE: The Scales of Injustice) The Vault was permanently kept dark, as some objects would react with light. (AUDIO: Tales from the Vault)

It was one of several storage facilities supporting the main Black Archive in the Tower of London. (AUDIO: The Screaming Skull)

History
The Vault was initially located in the Cheviot Hills in Northumberland. It was formed by Harold Wilson under the Ministry of Technology, ostensibly to help develop new technologies to enrich British industry: Wilson's "white heat of technology". In truth it located and used alien technology for its own ends, and the MPs who'd approved of it where unaware of what it did. It was run by a mysterious man called the General, who was in fact Brigadier Lethbridge-Stewart's brother James from the Inferno Earth. (PROSE: One Cold Step, Beast of Fang Rock, Mind of Stone)

Debris from the Shoreditch Incident and WOTAN had been sent to the Vault. (PROSE: The Scales of Injustice)

In the late 1960s, the remaining Yeti and technology left over from the London Event were transferred to the vault, including Anne Travers. (PROSE: The Forgotten Son) Corpses from the London Event were transferred there as well, so the "web" fungus could be taken off them. (PROSE: Beast of Fang Rock) A number of other corpses were taken to the Vault after subsequent alien attacks. (PROSE: The Scales of Injustice)

At that point the quartermaster of the vault was Captain Hawkins. (PROSE: The Forgotten Son) Leonard Harkness was a scientist who worked there during the late 1960s. (PROSE: One Cold Step) Another scientist who worked alongside Anne was Tim Gambrell, who assisted Anne in running tests on the Om-Tsor and the body of Ed Hill. Anne later revealed to Colonel Lethbridge-Stewart that she was at the Vault to gather information for General Hamilton. The remaining Rutan technology and shuttle pod was sent to the Vault following the events at Fang Rock in May 1969. (PROSE: Beast of Fang Rock) Shortly after, Colonel Lethbridge-Stewart and Air Vice Marshal Gilmore uncovered a secret bunker beneath Shoreditch, London, owned by the Vault. It was run by Lieutenant Leslie Johnston, and he was using a captured Professor Travers to control Yeti found in the Underground. Lethbridge-Stewart and Gilmore brought the operation to an end, but Johnston escaped. (PROSE: The Dogs of War)

By the early 1970s, Department C19 had taken over the Vault and forcibly retired James Gore. (PROSE: Ashes of the Inferno) The Pale Man ran the facility. The Vault's items had grown and even included the complete Mars Probe 6. The Pale Man intended to use the technology within to conquer Earth, and the Vault was raided by the Third Doctor and UNIT. (PROSE: The Scales of Injustice)

Brigadier Lethbridge-Stewart had other personnel inside the Vault following Anne Travers. (PROSE: Ashes of the Inferno)

In later years, UNIT had control over it. The contents of the Vault were moved to the Angel of the North in the 1990s. (AUDIO: The Screaming Skull)

In the 21st century, both Captain Ruth Matheson and Charlie Sato worked there. (AUDIO: Tales from the Vault) The Master escaped from the Vault after hypnotising Matheson and Sato into letting him escape in his TARDIS. (AUDIO: Mastermind) Rees later escaped from the Vault after possessing every carcass that had been stored in the Vault, in addition to UNIT soldiers who were sent in to investigate the occurrence. (AUDIO: The Screaming Skull)

Items
The vault stored a number of alien life forms, including a de-activated Imperial Dalek from the Shoreditch Incident, a new strain of Venus flytrap found in Rhodesia large enough to catch a rabbit or a small dog (PROSE: The Scales of Injustice), fragments of the Xylok crystal from Krakatoa (TV: The Lost Boy, PROSE: Beast of Fang Rock), and a deactivated Terravore. The Vault was also where the Master was imprisoned when he was captured by UNIT following his escape from the Eye of Harmony. (AUDIO: Mastermind). Other organic matter stored were Nestene "blood", a plague created by the Silurians, Krynoid pods, and fruit from Western Australia containing mercurial dioxide due to fallen particles of dust from outer space (PROSE: The Scales of Injustice). Also contained were a few weapons, including Cyber-guns, Excalibur, and Plastic daffodils. Other items stored in the vault were Meteorite globes from the first Auton invasion, WOTAN, Mars Probe 6, samples of Stahlman's ooze,  the wreckage from a Sontaran scout ship, an army jacket, a painting, crystal, a wax cylinder, (AUDIO: Tales from the Vault), The Master's TARDIS (AUDIO: Mastermind), and Rees' skull and music box (AUDIO: The Screaming Skull).

Bodies
There were also several human bodies sotred in the vault, belonging to George Ratcliffe, Melvin Krimpton, Stephen Weams, Mark Gregory, and George Hibbert. (PROSE: The Scales of Injustice)

Behind the scenes
When Gary Russell, the author of The Scales of Injustice, tweeted Mastermind writer Jonathan Morris, asking him if the Vault in Mastermind was the same as the one from Russell's novels, Morris responded, "Possibly, but it's now been moved to a secret base under [the] Angel of the North". When he realised Russell's C19 Vault was a short distance from the one in Mastermind, Morris stated that "it all fits!" AUDIO: The Screaming Skull later gave the in-universe link for this move.