Hitler is convinced the document is genuine, though Admiral Wilhelm Canaris, head of the "Abwehr", is skeptical. The Nazis dispatch Patrick O'Reilly (Stephen Boyd), a pro-German IRA spy, to London to investigate. O'Reilly investigates Martin's "fiancée", Lucy Sherwood (Gloria Grahame), who is the roommate of Montagu's assistant, Pam (Josephine Griffin). O'Reilly arrives at their flat, posing as Martin's old friend, on the same day Lucy received news that her real boyfriend was killed in action. Her genuine grief mostly convinces O'Reilly. As a final test, however, he gives Lucy his north London address, telling her to contact him if she needs anything. He then radios his German contacts saying that if he does not send another message in one hour, it means he has been arrested. As Montagu, General Coburn (Michael Hordern) of Scotland Yard's Special Branch and police officers are en route to O'Reilly's flat, Montagu realises why he left his address. Montagu convinces a reluctant Hordern to let O'Reilly go. After no one arrives to arrest him, O'Reilly sends a "Martin genuine!" radio message. The Germans then transfer most of their Sicily-based forces to Greece, making the Allied deception successful.