A maniac fan torments Masha Lemesheva, a talented blind singer, with threats on the phone. Mom's car goes to the police. They have a wiretap installed at their house, and Artyom and Mukhtar even stay in the apartment overnight. However, they fail to protect the girl from being attacked by a bandit in the entrance. Lena Brusnikina consults with a specialist psychologist from the Ministry of Internal Affairs and gives him a recording of a telephone conversation. The psychologist is sure that this is not a maniac, but a person pursuing quite rational goals.
 

It was decided to combine a series of burglaries into one case, as they are connected by two nuances. Firstly, robbers enter apartments not with the help of lock picks, but with the help of a key, and secondly, all robbed businessmen's wives visit the same aquacenter "Aquamarine". Lena, under the guise of a bored lady, and Artyom, with a desire to swim, go there. However, Mukhtar makes some adjustments to his plans: he hides the bathing trunks of his beloved master…