The owner of the famous Chaika restaurant in the city, Larisa Kotova, likes to solve detective riddles in her free time, and she copes with it no worse than professional detectives. But the problem that Larisa was given by her former classmate Lyudmila Politina seems to have a far from simple solution. Someone threatens her over the phone, assuring her that Politina will die on her birthday. The mysteries do not end there: her husband Andrei actually dies at the holiday, poisoned with potassium cyanide. How are their friends who came to the birthday party connected with this tragic event? The classic case is that only one of them could poison the husband. Or did Lyudmila herself do it? But the threatening calls did not stop even after Andrei’s death...