It is June 21st, the longest day of the year, and new mother Camilla’s life is about to change forever. After months of maternity leave, she will drop her infant daughter off at daycare for the first time and return to her job as a literary agent. Finally. But, when she wakes, her husband Luke isn’t there, and in his place is a cryptic note.

Then it starts. Breaking news: there's a hostage situation developing in London. The police arrive, and tell her Luke is involved. But he isn't a hostage. Her husband—doting father, eternal optimist—is the gunman.

What she does next is crucial. Because only she knows what the note he left behind that morning says...