Katya Beloborodko grew up in a small fishing village. She feels truly happy only at the helm of her father's boat "Assol" and next to her beloved dolphins. But the girl was proposed by the most enviable groom in the village, Sergey Galibin. With him, Katya will have a rich and settled family life, but the sea will have to be forgotten forever. Meanwhile, the new head of the scientific center for the study of the Black Sea, Mikhail Ratmanov, arrives from the capital. On the shore, he discovers a dead dolphin. A terrible discovery by a young scientist changes Katya's life forever - she becomes a suspect in a crime.