It's been 25 years since Tom Thorne last went to work wearing the 'Queen's cloth' but now, having stepped out of line once too often, he's back in uniform. He's no longer a detective, and he hates it. Still struggling to adjust, Thorne becomes convinced that a spate of suicides among the elderly in London are something more sinister. His concerns are dismissed by the Murder Squad he was once part of and he is forced to look into it alone. Now, unable to trust anybody, Thorne risks losing those closest to him as well as endangering those being targeted by a killer unlike any he has hunted before.