New York’s labyrinthine American Museum of Natural History becomes the site of more marvels, as the author of Falcon’s Egg (1995) sends fraternal twins Alice and Fig spinning into a diorama that is also a gateway in time and space. It’s a “bad, sad, mad” time for the twins, whose mother lies in a coma after an accident. Seeking some solace in roaming the halls of the museum where she works, the twins chance upon a window that isn’t glass, and find themselves in 1913 France, where a museum expedition is collecting rare specimens. Their attempt to return to their own time sends them further back—thousands of years, in fact, to meet Oomor, a friendly Neanderthal shaman who introduces them to another victim of the diorama, a genial museum artist named Hieronymous Quigley who has not only taught Oomor broken English, but turned him into an accomplished cave painter as well. Oomor also proves to have a will of iron, and though all three visitors are understandably reluctant to attempt another return to the 20th century, he chivvies them into trying. All ends well—better than expected, in fact, for by journeying into the past, the twins have changed the future, and among other pleasant surprises, their mother is awake and waiting for them. Despite the stressful family situation, this lightweight adventure, featuring bright ten-year-old protagonists, a colorful supporting cast, encounters with woolly mammoths and other extinct creatures, and more discomfort than outright danger, will provide an enjoyable ride for fans of science-tinged fantasy. (Fiction. 10-12)