Thirty-year-old Alice is a sailor. She leaves Félix, her man, on terra firma, and embarks as a mechanic on an old cargo ship, Fidelio. Once on board, she discovers that she is replacing a man who has just died and that Gaël, the first great love of her life, is the ship's captain.
In her cabin, Alice finds a notebook that belonged to her predecessor. What she reads therein -  mechanical problems, sexual conquests and melancholy love - curiously reflects her own journey.
The only woman amongst a male crew, lulled by her love affairs that start to reel and the camaraderie in ports of call, Alice exposes herself to the joy of living everything at once and trying to stay on course.