Aisling has a stomachache that won't go away. Her older sister, Celia, who's always told her everything, has run away without a word, without even saying goodbye. After three Long Terrible Weeks, a phone call has her family on the road to New York City. Police there have found Celia's ink-splattered bag. But they haven't found her. No matter. Aisling has a secret, a decision she won't dare let on to her parents. Once they arrive, she's going to run away, too. She's going to look for Celia, and find her, all by herself. Matilda has scribbled down every detail she can remember - of the moment she'd watched Celia disappear into a rock. Like the others. Like her son. Her friends have worked like an army of sleuths, year after year, gathering clues and bringing all to their underground cardboard town. What invisible monster is doing such a thing? Why won't anybody believe them? Will they ever have their loved ones back? Aisling's search for her sister leads her to the top of a New York City rock, to Matilda, to a discovery - she has a power. A special sight. If Celia and the disappeared are ever to be freed ... Aisling's sight is their only hope.