A parallel universe, a crystal cave, a talking mastodon, and one tough granny. The World Jumper has misfired and inventor-in-training Angus Clark finds himself in a primitive, snowy village with no running water, no electricity, and enormous animals that haven't roamed the earth for thousands of years. Together with the fearless Ivy Calloway, Angus must battle a prehistoric monster, rescue his little sister, and live in a tiny cottage full of ornery women.

Will Angus survive the most colossal dung heap he's ever seen? Can Ivy overcome a huge flea infestation? Will Angus ever find his invention? And what will become of the tranquil Clark household when a fierce hunter moves in?

The Crystal Lair is the second novel in the Inventor-in-Training series. Angus and Ivy have survived the pirates and now come face-to-face with prehistoric animals, harsh blizzard conditions, and the worst chores any child has ever endured. Along the way, Angus discovers that he'd do anything to protect his irritating little sister.