Twelve-year-old Olia knows a thing or two about secrets. Her parents are the caretakers of Castle Mila, a soaring palace with golden domes, lush gardens, and countless rooms. Literally countless rooms. There are rooms that appear and disappear, and rooms that have been hiding themselves for centuries. The only person who can access them is Olia. She has a special bond with the castle, and it seems to trust her with its secrets.

But then a violent storm rolls in . . . a storm that skips over the village and surrounds the castle, threatening to tear it apart. While taking cover in a rarely-used room, Olia stumbles down a secret passage that leads to a part of Castle Mila she's never seen before. A strange network of rooms that hide the secret to the castle's past . . . and the truth about who's trying to destroy it.