Cat lives in Los Angeles, about as far away as she can get from her estranged twin sister El and No. 36 Westeryk Road, the imposing gothic house in Edinburgh where they grew up. As girls, they invented Mirrorland, a dark, imaginary place under the pantry stairs full of pirates, witches, and clowns. These days Cat rarely thinks about their childhood home, or the fact that El now lives there with her husband Ross. But when El mysteriously disappears after going out on her sailboat, Cat is forced to return to the grand old house, which has scarcely changed in twenty years. No. 36 Westeryk Road is still full of shadowy, hidden corners, and at every turn Cat finds herself stumbling on long-held secrets and terrifying ghosts from the past. Because someone—El?—has left Cat clues all over the house: a treasure hunt that leads right back to Mirrorland, where she knows the truth lies crouched and waiting...