Caroline Walker is a happy-go-lucky, one-friended girl who has just turned nineteen. When she meets Harry Styles, Louis Tomlinson, Liam Payne, Niall Horan, and Zayn Malik, international spies, she learns that she must be brave to deal with the challenges that the bad guys throw at them. Can she help the boys defeat the villains, or will she break under the pressure to be braver than she ever has before?