First broadcast 25th April 1974.

Gunter Hellman, a student revolutionary, is allowed into Britain with his wife Gisela to continue his studies.

George Sewell ... Detective Chief Inspector Alan Craven
Patrick Mower ... Detective Chief Inspector Tom Haggerty
Frederick Jaeger ... Commander Fletcher
Damien Thomas ... Gunter Hellman
Ann Firbank ... Gisela Hellman
Keith Buckley ... Martin Kingswood
Susan Tebbs ... Dr. Barbara Latimer
Patrick Troughton ... Professor Frederick Denny
Gareth Thomas ... Steve Ryman
Susan Jameson ... Detective Sgt. Mary Holmes
Peter Cellier ... Sir Terence Gabon
Paul Antrim ... Detective Sgt. Maguire
Donald Eccles ... Bishop Garnett-Templeton
Geoffrey Lumsden ... Appeal Chairman
Susan Richards ... Mrs. Ryman
Michael Guest ... TV Reporter