Persons Unknown is second in the DS Manon series, where we follow Manon Bradshaw after she has adopted Fly Dent, gotten pregnant, and left the murder squad. She's taken on cold cases to avoid strenuous duty, but it seems she has buyer's remorse. It is obvious that she'd prefer to be working on active cases, and her opinion of her former partner, Davy, and his new lead are less than kind. Steiner touches on current issues of race - Fly, twelve, is aware that he is frequently stopped and questioned or searched because he is a black, teen boy giving Manon reason to move out of London. Manon, Fly, Manon's sister, Ellie, and her nephew, Solly, all move in together. Fly becomes Ellie's defacto baby sitter, which leads to irritation and judgment from Manon. Fly is resentful of the move, and maybe of Manon's pregnancy, and he starts to pull away, despite her attempts to pull together.
When a man stabbed in a nearby park turns out to be her nephew's father, and Fly becomes the number one suspect, Manon must figure out how to help her son, who is pushing her away, while working outside of the department investigating him. Manon's relationship with her sister also becomes strained, as she comes to realize her sister is hiding something, and won't account for her whereabouts during the day her ex died. She also comes to learn that the victim had been treating Fly poorly, which further strains her relationship with her sister. The relationship of the victim to Manon and her family lead to a lot of tensions between Manon and her ex-partner as well. Steiner does a great job of portraying the very real struggle and tensions between friends and family members, especially when they are stretched to their breaking point.