Scientist Boris Turganev (Murray) has defected from Russia and is now working for the British. As Boris struggles to make his superiors at a government nuclear research lab believe he's there to work and not to spy for the Russians, an office romance blossoms that could put his mission in jeopardy. But what exactly is that mission?
Stephen Murray as Boris Turganev
June Thorburn as Leila
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 Doctor 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
Derek Francis as Police Inspector (uncredited)
The New York Times called the film, "a TEPID, square-cut espionage drama."
AllMovie wrote, "While only 71 minutes, Master Spy has enough plot twists for a library-full of Fleming and LeCarre."