In Pedra da Lua, a paradisaical city by the sea, the old journalist Álvaro keeps radio 74.5 Uma Onda on the air, radiating hope, humour and high spirits. The starting point is the arrival of Luiza, the radio host's granddaughter, who returns after suffering a severe disappointment in her marriage to Caíque. Starting a new life again, the young woman falls in love with Miguel, an ex-boyfriend who lives on a boat and lives taking tourists out.
Miguel is the son of a fisherman and has been passionate about the sea since he was a boy. As a child, he and Luiza dated. They both believe that, in past lives, he would have been a porpoise, and she was a mermaid. For socioeconomic reasons, both had to choose different lives. He got a scholarship and went to study marine biology in the United States; Luiza ended up marrying the ambitious and manipulative Caíque.
Unhappy with her marriage and life in the big city, she returns to the paradisaical Pedra da Lua, to look for her grandfather Álvaro, and ends up meeting her old love again.
