While the technical problems are being solved, investigations are undertaken to thwart foreign espionage, especially from communist sympathizers who might be associated with socialist organizations. The snooping reveals that Oppenheimer has had a young mistress, Jean Tatlock, and he is ordered by Groves to stop seeing her. After he breaks off their relationship without being able to reveal the reasons why, she is unable to cope with the heartache and is later found dead, apparently a suicide.