The Russian detective series "Duet by Law" tells the story of friendship and rivalry between two experienced investigators. Major Tatiana Titova returns to her hometown from the capital and is transferred to a local investigative committee as a regular operative. This decision surprises her colleagues, as she used to lead a department in Moscow. Her former friend and new boss, Alla Davydova, has her own version of events. Once upon a time, the women fought over the same man. Alla is convinced that Tatiana has returned to take her husband away from her.