The Doomsday Contract (in-universe)

The Doomsday Contract was an unproduced Doctor Who serial written by John Lloyd. It was later released as an audio play by Big Finish, starring Tom Baker, Lalla Ward, John Leeson, and Julian Wadham, and was written by John Lloyd and Nev Fountain. (WC: Tom Baker stars in John Lloyd's lost Doctor Who adventure, The Doomsday Contract)

Important note
This is an in-universe counterpart of the real world Big Finish audio drama The Doomsday Contract.