In 1943 the family home in Berlin was rendered uninhabitable by an air raid and the Klinglers moved permanently to the small country estate at , just outside Osterburg (Altmark), which Margarethe had inherited after her father died in 1931. While they were living here Karl Klingler's desk was searched by the Gestapo and he was interrogated about his friends Max Planck and Erich Vagts. His address book was confiscated: it included contact details for his friend's son Erwin Planck, who around this time was sentenced to death for involvement in a widely reported conspiracy to assassinate the leader. According to testimony of former local government officials, Klingler's mail was subject to police monitoring while he was living in Krumke. As the war drew to an end he became the subject of a Gestapo arrest warrant because he was identified as a "flight risk", but the warrant could not be executed before the area was over-run by allied forces as the war ended, formally in May 1945.