The Prince of Mist — Carlos Ruiz Zafon

It's war time, and the Carver family decides to leave the capital where they live and move to a small coastal village where they've recently bought a home. But from the minute they cross the threshold, strange things begin to happen. In that mysterious house still lurks the spirit of Jacob, the previous owners' son, who died by drowning.

With the help of their new friend Roland, Max and Alicia Carver begin to explore the strange circumstances of that death and discover the existence of a mysterious being called the Prince of Mist--a diabolical character who has returned from the shadows to collect on a debt from the past. Soon the three friends find themselves caught up in an adventure of sunken ships and an enchanted stone garden--an adventure that will change their lives forever.