Whistle in the Dark — Emma Healey

Jen's fifteen-year-old daughter goes missing for four agonizing days.

When Lana is found, unharmed, in the middle of the desolate countryside, everyone thinks the worst is over. But Lana refuses to tell anyone what happened, and police draw a blank. The once-happy, loving family return to London where things start to fall apart. Lana begins acting strangely: making secretive phone calls, hiding books under her bed, sleeping with the light on.

As Lana stays stubbornly silent, Jen sets out to solve the mystery behind her daughter's disappearance herself...