The Lantern Men

Everything has changed for Dr Ruth Galloway.
She has a new job, home and partner, and 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 travellers 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?