Gr. 4-7. What if Alice fell down an air vent in a New York City apartment building instead of down a rabbit hole? Collins considers a similar possibility in her exceptional debut novel, a well-written, fast-moving, action-packed fantasy. Eleven-year-old Gregor expects a long, boring summer of baby-sitting his two-year-old sister, Boots, and his senile grandmother. Distracted with thoughts about his father, who disappeared three years ago, Gregor belatedly notices that Boots has crawled into an air vent in the laundry room. He dives in after her, and the two are sucked downward into the Underland, a fantastic subterranean world of translucent-skinned, violet-eyed humans, and giant talking cockroaches, bats, spiders, and rats. Eventually, the terrified Gregor is transformed into a warrior hero who leads a successful battle against an army of invading rats and discovers his father, who has long been held prisoner by the enemy. Collins creates a fascinating, vivid, highly original world and a superb story to go along with it, and Gregor is endearing as a caring, responsible big brother who rises triumphantly to every challenge. This is sure to be a solid hit with young fantasy fans.