Guerisse was a Belgian doctor and an undercover agent who ran an escape route in southern France. Guerisse had been a medical officer in the Belgian Army but had come to Britain after Dunkirk. He assumed the identity of Pat O’Leary, a French Canadian, and joined the Royal Navy. While on an operation which the Fidelity conducted for the Special Operations Executive in the south of France, he was left behind by accident and arrested. He escaped and made contact with an escape organization run by the Scotsman, lan Garrow, which had been set up to evacuate British troops left in France after Dunkirk. When its leader was arrested, Guerisse took over and built up the organization. He helped about 600 members of Allied forces to escape in one year without receiving much help from London; it was only in July 1942 that Guerisse got a M19 wireless operator. His organization was not very security-conscious and all the leaders knew each other so by the end of 1942 many of them were on the run. In March 1943 Guerisse was betrayed by a double agent and arrested at Toulouse. He was tortured and imprisoned and spent the war in Dachau. On 29 April 1945 he was liberated and received a George Cross in recognition of his services.