When a prominent French politician is found dead on the border between the UK and France, presumably under the sea, detectives Karl Roebuck and Elise Wassermann are sent to investigate. The police are forced into an uneasy international alliance after a shocking crime scene discovery.

While Elise Wassermann and Karl Roebuck are back to investigate the case of a French couple who are abducted from the Eurotunnel, the case gets complicated by a plane crash into the Channel.

A stolen fishing boat found adrift and on fire in the English channel turns into a new case for Karl and Elise. Together and apart, they are forced to grapple with decisions they have made and must make decisions that cut to the deadly heart of the matter: what is the value of a single life?