Security guard Sonja wakes up locked in a robbed bank vault with a hole in her memory. Inspectors Deja and Jaka believe she is involved in the robbery. There is no sign of a break-in, and Sonja kept her criminal record secret when she got the job. Mayoral candidate Gabrijelčič is surprised by the news of the robbery in the middle of the campaign, bank director Alenka is under pressure from her clients, and Sotler from the insurance company tries to get information from the police. Sonja promised her son that she would return, but all she remembers is a sound that she cannot explain.