George Murphy as Inspector James 'Jim' Belden

Finlay Currie as Professor Albert Kafer

Virginia Gilmore as Millie / Teresa Zalenko

Karel Stepanek as Alexi Laschenkov / Gregory Anders

Louisa Horton as Mrs. Elaine Wilben

Peter Capell as Chris Zalenko / Gino

Bruno Wick as Luther Danzig

Jack Manning as Melvin Foss / Vincent

Karl Weber as FBI Agent Charlie Reynolds
George Roy Hill as Nicholas Wilben

This cross between documentary and spy thriller was written during the “Red Scare” years, and focuses on the efforts of the FBI to cover up a security leak. It tracks federal agent Belden as he tries to find the communist spies who threaten endangerment of the sovereignty of the United States.