Antonio and Estrella are siblings and industrial divers working the port of Huelva, next to a sprawling petrochemical plant.

He does the dangerous underwater repair work that keeps the port running; she studies marine life and dives alongside him, still hoping for the marine-conservation career she's long put on hold — first for their demanding father, now for her scatterbrained older brother.

When Antonio's ex-wife threatens legal action that could cost him custody of his daughters, financial desperation pushes him toward a way out: a hidden cache of cocaine lodged in a tanker's hull. What looks like salvation threatens to pull both of them under.