Something's not right at number 56 Water Street. From the sidewalk in front of the abandoned house, ten-year-old best friends Derek and Ravine watch lights flicker on and off, again and again. When they race home to tell their parents, they're in for a shock: there is no house at 56 Water Street! The house is invisible to everyone but Derek and Ravine, and the ghost haunting the old place wants to get their attention. Trapped for more than a hundred years, Isabel Roberts needs to solve the mystery of her younger sister's fate before she can truly rest in peace. And she's chosen Derek and Ravine to help her. When the two friends summon the courage to venture inside the house, they're unprepared for what they find (after all, meeting a ghost face-to-face isn't exactly normal) and for the spine-tingling adventures in store for them. But Derek and Ravine are determined to help Isabel. If they don't, she could be a ghost forever!