The Lantern Men by Elly Griffiths

Forensic archaeologist Ruth Galloway changed her life—until a convicted killer tells her that four of his victims were never found, drawing her back to the place she left behind.

Everything has changed for Ruth Galloway. She has a new job, home, and partner, and she is no longer north Norfolk police’s resident forensic archaeologist. That is, until convicted murderer Ivor March offers to make DCI Nelson a deal. Nelson was always sure that March killed more women than he was charged with. Now March confirms this and offers to show Nelson where the other bodies are buried—but only if Ruth will do the digging.

Curious, but wary, Ruth agrees. March tells Ruth that he killed four more women and that their bodies are buried near a village bordering the fens, said to be haunted by the Lantern Men, mysterious figures holding lights that lure travelers to their deaths.

Is Ivor March himself a lantern man, luring Ruth back to Norfolk? What is his plan, and why is she so crucial to it? And are the killings really over?