Persons Unknown is the second police procedural following Detective Sergeant Manon Bradshaw, following up Missing, Presumed. Manon's character is growing and changing throughout. She is five months pregnant at the start. And she has adopted Fly Dent, a quiet teenager whose family died in the previous book. Looking for a change of pace in their hectic life and a better quality of friends for Fly, they move from London to Cambridgeshire with Manon's sister, Ellie, and her toddler son, Solly.