It is Summer, 1943. At this time of year our submarines cannot operate in northern waters: there is no darkness to provide cover when surfacing. Yet H. M. Submarine Setter is sent North. It makes sense to nobody. Least of all to Lief Oldsen, Sub-Lieutenant in the Royal Norwegian Navy, whose sudden appointment to Setter is shrouded in mystery. On this hazardous expedition, the hunter becomes hunted and tension turns to cold terror.