First broadcast 13th June 1973.
A physician is under surveillance as a possible security risk.
George Sewell ... Detective Chief Inspector Alan Craven
Roger Rowland ... Detective Sergeant Bill North
Annette Crosbie ... Sarah Lovett
Roger Hume ... Dr. Ted Lovett
Sheila Scott Wilkinson ... Pam Sloane
John Arnatt ... Denning
Beth Harris ... Andrea Watkins
Seymour Green ... Bank Manager
Tim Barrett ... Grindley
Malcolm Terris
John Cazabon
Neal Arden
Toby Lenon
Diana Rayworth ... Bookshop Proprietor (as Diana Raworth)
Julie Martin ... Hotel Receptionist
Anthony Woodruff
Reg Thomason ... Thompson
