In the Late Cretaceous, a great inland ocean divided North America in two. A curious and adventurous dolichorynchops (familiarly known as a 'dolly') travels through life's stages, experiencing the world from her spot near the bottom of the food chain. Along the way, she'll encounter long-necked pleisosaurs, giant turtles, enormous fish, ferocious flippered crocs, fierce sharks, and the most dangerous sea monsters of all, the mosasaurs.