The Crime of the Century
was due to be one of the serials for the unproduced 1990 series of Doctor Who, starring Sylvester McCoy as the Seventh Doctor. His companion was due to be a girl who he had delivered as a baby in the 1960s-set story Ice Time (i.e. the episode from the week before).
Quite who was due to write this story is not known, so I've picked Rona Munro as it is fitting that the author who finished off the series should also bring it back, in a sense. The plot of this story is unknown, save for the opening scene.
The Doctor's would-be companion is an international safe cracker, skills she has inherited from her father, an underworld mobster with a recurring role likened to a "dodgy Brigadier". She works her way around a posh party in an English country house, eventually reaching an unguarded safe. She cracks the combination and the safe opens... then the Doctor hops out, and cheerfully says "What kept you?"
Questionable copyright. Doctor Who and related images (C) the BBC; "The Crime of the Century" probably (C) whoever the original author would have been; main image is taken from "Endgame", a documentary on the DVD release of "Survival" (1989).