Marco's Millions

When Marco's shy and fragile little sister, Lilly, tells him about the strange lights in the basement, he thinks she's imagining things. But Marco is curious, and before long he investigates. He finds a passage into a strange world, where he meets insect-like creatures who seem to know all about Lilly. They believe she is special and beg Marco to bring her to them so that she can embark on a dangerous quest to save their world from ruin. Can Marco help the creatures while protecting Lilly from harm? "Sleator achieves some dazzling effects here."(The Horn Book, starred review)