His last hiding place was in an apartment with his university friend Lion Nordheim, his wife Jeanne, and her sister Trusha van Amerongen. In the course of his hiding he kept in touch with the scientific community through visits at his hiding place by Hendrik Anthony Kramers and Lambertus Broer. Jeanne and Trusha had blond hair and blue eyes and ventured out in public as non-Jews, while Lion and Pais hid in the apartment. In March 1945, however, they were betrayed and all four were arrested. The same week the Americans had crossed the Rhine and cut the rail lines, making impossible their transfer to a concentration camp. The women were soon released. After a month of interrogation by the Gestapo, Pais was released several days before the end of the war. Nordheim was executed ten days before the end of the war.