Piero is a dentist who lives separately from his wife Roberta. To spend the traditional two-week holiday with his children Fiorella and Claudio, he decides to buy a boat called Biba, Roberta's nickname, with which to leave Civitavecchia for Sardinia. Roberta also arrives from Milan to join them on the Kabir, a yacht owned by engineer Casorati, frequented by wealthy people, including Attilio.
The start of the holiday for Piero is not the best: the Biba actually turns out to be a sort of semi-abandoned boat that, as soon as it is delivered, immediately loses its propeller, forcing Piero to dive into the water to retrieve it. After travelling only a few miles, they have to return to Civitavecchia because of an accident involving the net of a group of fishermen. They eventually land on the Argentario coast, but Roberta is worried about her children and decides to leave the Kabir to join Piero and the boys on the Biba.
Despite numerous difficulties encountered during the voyage, the Biba finally reaches Sardinia, and this brings Piero and Roberta closer together. However, in Porto Cervo, Piero meets Alessia, his nurse and lover, who asks him for a favour to be recommended by a well-known dentist. Piero contrives an excuse to attend a dinner with Alessia, but is discovered by Roberta. After yet another argument, the two realise they still love each other and decide to get back together.
Meanwhile, the Biba drifts away from the coast, but Piero and Roberta manage to reach it in a rubber dinghy. Unfortunately, they find themselves hostages of two prison escapees who have taken the boat to Corsica. However, the pair manage to outsmart the two escapees. Meanwhile, Claudio and Fiorella, believing that their parents have been killed by bandits, sink the Biba. Stranded in the middle of the sea, they are fortunately rescued by Attilio. In the end, Piero and Roberta can finally start their life together again, perhaps thinking of buying a bigger boat.