Fisheries officer Simone Lord is transferred to Quebec's remote Magdalen Islands for the winter, and at the last minute ordered to go aboard a trawler braving a winter storm for the traditional grey seal hunt, while all of the other boats shelter onshore. Detective Sergeant Joaquin Moralès is on a cross-country boat trip down the St Lawrence River, accompanied by Nadine Lauzon, a forensic psychologist working on the case of a savagely beaten teenager with Moralès' old team in Montreal. When it becomes clear that Simone is in grave danger aboard the trawler, the two cases converge, with startling, terrifying consequences for everyone involved . . .