Master Spy (also known as Checkmate)^[2][3] is a 1963 British spy film directed by Montgomery Tully and starring Stephen Murray, June Thorburn and Alan Wheatley.^[4] The film was based on the short story "They Also Serve" by Gerald Anstruther and Paul White.

The US release film poster identifies the Master Spy as Agent 909.

A Russian nuclear scientist, Dr Boris Turganev, defects from an unnamed country to the West. He is employed by the UK Government at a top secret scientific establishment to continue his work on neutron rays. He is introduced to a wealthy local man, Paul Skelton, and they identify themselves to each other as spies. Turganev's colleagues start to suspect he is stealing secrets for the communists; Turganev passes information to Skelton under the cover of their private games of chess. British Intelligence arrests them, and they are tried and sentenced to long prison terms.

Turganev's colleague is puzzled that the secret document which Turganev was passing to Skelton had been altered and would not work. In a plot twist, it is revealed that Turganev was working for British Intelligence, who suspected Skelton and wanted to catch his spy ring. A prison escape is engineered for Turganev so that he can return to his own country and continue his activities for the British with his cover intact.

• Stephen Murray as Boris Turganev
• June Thorburn as Leila Telford
• Alan Wheatley as Paul Skelton
• John Carson as Richard Colman
• John Bown as John Baxter
• Jack Watson as Captain Foster
• Ernest Clark as Doctor Pembury
• Peter Gilmore as Tom Masters
• Marne Maitland as Doctor Asafu
• Ellen Pollock as Dr Mary Morrell
• Hugh Morton as Sir Gilbert Saunders
• Basil Dignam as Richard Horton
• Victor Beaumont as Petrov
• Hamilton Dyce as Airport Controller
• Michael Peake as Barnes
• Dan Cressey as Policeman (uncredited)
• Derek Francis as Police Inspector (uncredited)
• John G. Heller as Police Officer (uncredited)
• Aileen Lewis as Woman boarding a plane (uncredited)
• John H. Watson as Detective at airport (uncredited)^[5][6]

• The New York Times called the film "a TEPID, square-cut espionage drama."^[7]
• AllMovie wrote, "While only 71 minutes, Master Spy has enough plot twists for a library-full of Fleming and LeCarre."^[8]