Monsters — Emerald Fennell

The beautiful seaside town of Fowey is not as idyllic as it might seem. The body of a young woman is discovered in the nets of a fishing boat. It is established that the woman was murdered. Most are shocked and horrified. But there is somebody who is not—a 12-year-old girl. She is delighted; she loves murders. Soon she is questioning the inhabitants of the town in her own personal investigation. But it is a bit boring on her own. Then Miles Giffard, a similarly odd 12-year-old boy, arrives in Fowey with his mother, and they start investigating together. Oh, and also playing games that re-enact the murders. Just for fun, you understand. A book about two 12-year-olds that is definitely not for kids.