It’s Camilla’s first day back at work, her daughter’s first day at nursery. But husband Luke is nowhere to be seen. The only trace of him is an unfinished note. Camilla tries to put it out of her mind; there must be a rational explanation. Then it starts. Breaking news: there's a hostage situation developing in London. The police arrive: Luke is caught up in it. But he isn't a hostage. Luke - doting father, successful writer, enthusiastic runner and eternal optimist - is the gunman. What Camilla does next is crucial. Because only she knows what the note he left behind says, and the clues it might hold . . .