Lieutenant Bradley Heap has gone AWOL and taken along his wife and son. They're managing to cope just fine until an encounter with a gang of drug dealers turns their world upside down. Detective John Locke of Police Scotland joins forces with the Navy police in the search for Heap on a trail that will take them from the middle of Scotland to the edge of England's Lake District. The Shallows explores the limits of human endurance and examines how far people will go to protect the ones they love.