Criminal Police Commissioner Sabina Nemez is extremely surprised to meet a woman in monastic garb in the main building of the BKA in Wiesbaden, who declares her desire to confess to a crime. And not to anyone, but exclusively to Sabina's colleague Marten S. Sneijder. But after a heated discussion with the new head of the BKA, he quit, so Sabina has to replace him. From what she hears, she takes her breath away: a seemingly harmless woman declares that she will commit seven murders in the next seven days - she remains silent about the motive and method. An elderly nun is apprehended, and the BKA is in turmoil, especially after Sabine, despite her best efforts, fails to prevent the first murder. It soon becomes clear that behind all this lies an extremely sophisticated plan, which also intrigues Sneijder. He returns to the BKA and, together with Sabina, gets involved in the game of a nun, not suspecting into what dark abysses this time an unpredictable rival will involve him ...