During his stay in France he got involved with the French Resistance. His fellow Resistance members praised him for his bravery, but they also noticed his psychotic tendencies. Lindemans was prone to violent outbursts and seemed to take pleasure in killing people. He therefore never gained the full trust of his fellow Resistance members. The following years Lindemans performed various jobs for the French, Belgian and Dutch Resistance before returning to Rotterdam in 1944. There he found that his brother had been taken prisoner for helping Allied servicemen. In order to save his brother, Lindemans started working for the German intelligence service, called the Abwehr. As an informant Lindemans betrayed a large number of resistance members. At the beginning of September 1944 Lindemans was in Antwerp, fighting alongside the Allied forces to maintain his cover of a resistance fighter. Because of his background with the Resistance the Allied intelligence services sent him on a mission to the Netherlands. Unbeknown to the Allies Lindemans used this opportunity to inform the Germans about the Allied plans for Operation Market Garden that he had learned about during his stay in Antwerp. His information was however not taken seriously by the Germans, who still mistrusted him because of his resistance activities in the past. Therefore Lindemans’ betrayal had no influence on the outcome of Operation Market Garden. In October 1944, about a month after Operation Market Garden, Lindemans was betrayed and arrested by the Allies. He spent the rest of the war in prison and eventually committed suicide on 26 July 1946, awaiting his trial.