A warp ellipse draws the TARDIS off course. The Fifth Doctor's companions are separated from him not in space, but in time, and he has to deal with a treacherous schoolboy named Turlough. But why does the Doctor's old friend, the Brigadier, not remember him at all?
Peter Davison
as The Doctor
Sarah Sutton
as Nyssa
Janet Fielding
as Tegan Jovanka
Mark Strickson
as Vislor Turlough
Nicholas Courtney
as Brigadier Alistair Gordon Lethbridge-Stewart
Valentine Dyall
as The Black Guardian
David Collings
as Mawdryn
Angus MacKay
as Headmaster
Stephen Garlick
as Ibbotson
Roger Hammond
as Dr. Runciman
Sheila Gill
as Matron
Peter Walmsley
as Mutant
