In a parallel England, the Doctor tries desperately to convince his captors of the immense peril they are in. But they are convinced he is a spy. And penetration zero is getting close…
Quest roles:
Nicholas Courtney(Brig. Lethbridge-Stewart), Derek Newark(Greg Sutton), John Levene(RSM Benton), Sheila Dunn(Telephone Operator), Ian Fairbairn(Doctor Chester), Roy Scammell(RSF Sentry), Olaf Pooley(Professor Stahlman), Christopher Benjamin(Jago)