A Black Notice means one thing: unidentified human remains. And this time, five skeletons lie interlocked in the darkness of a wartime pillbox.

Rowan Jackman and Marie Evans are the detectives who take on the toughest cases on the Lincolnshire fens. And trouble always comes in threes.

6 a.m. on a dark autumn morning. Retired detective Bob Ruston is about to feed the dog when the doorbell rings. The man on the doorstep has blood running down his cheek and a look of terror on his face. ‘Please! Let me in! They’re going to kill me!’

Bob sees a handcuff dangling from the man’s lacerated wrist.

Later that day, a stylishly dressed woman marches into Saltern-le-Fen police station demanding to see Detective Marie Evans. ‘I want you to find my husband.’

Then a homeowner clearing undergrowth in his back garden makes a horrifying discovery. The decomposing remains of five bodies tangled together in an old WW2 pillbox.

Detective Jackman asks Interpol to issue a Black Notice. But little is he prepared for the shocking results that come in . . .