Kelsey Platt is a sixteen-year-old girl who is first mentioned in the story because she has sent Strike a letter asking for his advice on how best to cut off her leg. As it turns out, she’s a sufferer of body integrity identity disorder, and also as it turns out, she’s the first murder victim in the book. 

Physically, Kelsey is described as having a face that is chubby and plain. She lived in the Finchley area of London with her half-sister, Hazel Furley, and Hazel’s boyfriend, Ray Williams. According to Hazel, Kelsey was a compulsive liar, so it’s difficult for Strike and Robin to investigate Kelsey’s last-known whereabouts and who she was with. For example, she claimed to have a boyfriend named Niall, but she also had a crush on Niall of the boy band One Direction, so the veracity of her claim to have an actual boyfriend is in doubt.

In the TV series adaptation, Kelsey is portrayed by actress Fern Deacon.