Talented mathematician Anna Nikolaevna Shvabrina works as a school teacher. By the will of fate, she begins to help Captain Vershinin investigate complex crimes using mathematical methods. The main tools of the investigator are many years of experience and the basics of forensic science, Anna Nikolaevna is an impeccable knowledge of mathematical methods, formulas and models. It would seem that they are completely different, but it is thanks to this union that it will be possible to investigate the most difficult cases.