This was meant to be the perfect trip. The northern lights. A press launch on a luxury cruise ship. A chance for travel journalist Lo Blackwood to recover from a traumatic break-in that has left her on the verge of collapse and to work out what she wants from her relationship.

Except things don't go as planned. Woken in the night by screams, Lo rushes to her window to see a body thrown overboard from the next-door cabin. But the records show that no one ever checked in to that cabin, and no passengers are missing from the boat.

Exhausted, emotional and increasingly desperate, Lo has to face the fact that her sleep problems might be driving her mad, or she is trapped on a boat with a murderer - and she is the sole witness....