Returning to her gothic childhood home in the wake of her estranged twin's disappearance, Cat uncovers long-held secrets involving her sister's left-behind clues and a mysterious treasure hunt. Cat lives in Los Angeles, far away from the imposing gothic house in Edinburgh where she and her estranged twin sister, El, grew up. As girls, they invented Mirrorland, a dark, imaginary place under the pantry stairs full of pirates, witches, and clowns. El still lives at their old house, with her husband Ross. When El disappears after going out on her sailboat, Cat is forced to return after twenty years. The grand old house is still full of shadowy corners, and at every turn Cat finds herself stumbling on long-held secrets and terrifying ghosts from the past-- a past that leads right back to Mirrorland, where she knows the truth lies crouched and waiting. -- adapted from jacket