The Serial Killer's Sister by Alice Hunter

Despite a childhood in the care system, Anna Price has beaten the odds and built for herself the perfect life, complete with beautiful seaside home, devoted husband and a job she loves.

Then a policeman appears at Anna’s door: her estranged brother Henry is a wanted serial killer. For the past three years, a woman has been murdered on two specific dates – one of which is Anna’s birthday. The second is now only four days away, and the police need Anna’s help to catch Henry before he strikes again.

Then an envelope turns up on her doorstep and suddenly Anna finds herself caught in a sick game, one that she remembers all too well from childhood – one that, this time, she must win at all costs…