Nadezhda Lebedeva had a phenomenal instinct for crime, as well as an irrepressible curiosity that always prevailed over common sense. It seemed like trouble was looking for her on its own. So this time, Nadezhda Nikolaevna found herself at the center of an investigation into a non-trivial crime. An ordinary English teacher from an ordinary St. Petersburg school was found strangled in her apartment. There are no witnesses to the crime, no evidence. Who could be bothered by a quiet, nondescript woman, whose whole life boiled down to checking the notebooks of careless high school students and conjugating irregular English verbs? However, Nadezhda Nikolaevna found out that the murdered teacher was not at all the person she claimed to be and was leading a double life. Who was really hiding under the mask of a gray mouse? Where and behind what locks is the secret of the true, and not fake, life of a school teacher kept?