Andy travels back in time 149 million years, to the time of the ammonites - a kind of mollusc that lived in shoals and swam in the sea. His mission is to find an ammonite shell to replace the one he broke back at the museum. Along the way he witnesses bay turtles hatching and taking their first swim and comes face to face with eustreptospondylus, a swimming dinosaur. But, will Andy succeed before the museum opens?