On the high seas, a sailor is murdered on a Swiss merchant navy cargo ship. Aurélie Mercier, a former inspector transferred to the municipal police, returns to duty and goes to Cape Town to repatriate Florian, a suspect who is accused by everyone. He proclaims his innocence and says he is looking for Julia, his girlfriend.

The cargo ship is about to set sail. Aurélie, following her instincts, decides to stay on board with Florian. At sea, faced with an evasive captain and a hostile crew, she searches for the real murderer and understands that Julia's ghost is haunting the cargo ship.

An unexpected witness gives a new twist to the investigation, while a strange crate must be transferred to a ship in distress. For Aurélie, each answer leads to more questions and, as she seems to be getting to the truth, a new tragedy looms...

Tensions rise, as Aurélie understands that in addition to a murder, the cargo ship is transporting prohibited goods. She no longer knows who to trust, but in a final confrontation she reveals the truth about what happened to Julia.