In a hotel room, the body of the famous mathematician Lungin is found, and a precious gem worth a fortune is stolen from his safe. The night before, while under the influence of alcohol, Lungin told the students of Barkovskaya that the safe's code can be opened using ten numbers related to Pythagoras. Kartashova suspects four individuals: Andrey, Stanislav, Oleg, and Marina. Each of them lacks an alibi. However, Olga calculates the code numbers and discovers the real culprit!