Like her father, Ally is fascinated by the way that modern science and the study of dinosaur bones and fossils can lead to uncovering the mysteries of what dinosaurs were really like -- what they looked like, how they moved, how and what they ate and how they raised their young. But while Ally would love to accompany her father on his dinosaur digs, she has to settle for giving tours as a museum guide, and bringing her own theories about dinosaur evolution to life in her science project.

When Donald Hayden and his assistant Elizabeth (Kari Coleman) bring his latest discovery back to the musuem, Ally is excited that the oblong-shaped fossil rock might be a Tyrannosaurus egg, finally giving proof to the theory that the enormous theropod dinosaur was an evolutionary precursor to today's birds, and would therefore have exhibited parental behavior. Donald is not so quick to jump to that conclusion, but before he can complete his discussion with his teenage daughter, he is called away from his office.

Ally is alone and waiting for her father to return when an accident in the museum lab mysteriously sets her on an adventure in which Ally's present world begins to meld with the deep past. As she wanders into the museum, the bones of the T. rex skeleton suddenly appear to grow skin and muscle and the extinct creature lunges to life. When Ally retreats, she is hurtled through time, backwards to the terrain and territory of dinosaurs that are bigger than her imagination.