Nigel Pry leads the hunt for the Fifth Man, the Whitehall Mole, the Moscow Sleeper and the Gentlemen's Toilet - as the radio team asks the question "MI5 - Friend, foe or motorway?".
Starring Morwenna Banks, Angus Deayton, Geoffrey Perkins, Philip Pope and Michael Fenton-Stevens.
Music by Philip Pope and Steve Brown.
Written by Angus Deayton and Geoffrey Perkins.
Producer: David Tyler
First broadcast on BBC Radio 4 in September 1987.