Detective D. D. Warren is hard to surprise. But a lone woman outside D.D.'s latest crime scene shocks her with a remarkable proposition: Charlene Rosalind Carter Grant believes she will be murdered in four days. And she wants Boston's top detective to handle the death investigation.

Charlie tells a chilling story: Each year at 8:00 p.m. on January 21st, a woman has died. The victims have been childhood best friends from a small town in New Hampshire; the motive remains unknown. Now only one friend, Charlie, remains to count down her final hours.

But as D.D. quickly learns, Charlie Grant doesn't plan on going down without a fight. By her own admission, the girl can outshoot, outfight, and outrun anyone in Boston. Which begs the question, is Charlie the next victim, or the perfect perpetrator? As D.D. tracks a vigilante gunman who is killing pedophiles in Boston, she must also delve into the murders of Charlie's friends, racing to find answers before the next gruesome January 21st anniversary. Is Charlie truly in danger, or is she hiding a secret that may turn out to be the biggest threat of all?