The dentist of the provincial town of Upper Yamki made an unexpected scientific discovery by finding the thirty-third tooth in the patient’s oral cavity, Ivan Sergeyevich Travkin. Travkin, exhausted from pain, was taken to Moscow. Ivan Sergeyevich first becomes a patient of a madhouse (thanks to envious persons), and then — a hero of a scientific international conference and, finally, a patient of a dentist professor Bruk.