The actor and writer is magically transported back in time to chart the 180-million-year story of the prehistoric creatures, beginning by going back 155 million years to the Jurassic period. He explores the conifer forests and fern prairies that were their home, encountering a monstrous plant-eating diplodocus and deadly predator the allosaurus. Expert Susie Maidment arrives to decode these dinosaurs' remarkable behaviour, including the diplodocus

The actor finds himself transported back to a huge forest 68 million years ago in the late Cretaceous period, home to deadly predator Tyrannosaurus rex. With the help of expert Dr David Hone, Stephen observes a T-rex on the rampage, crunching up huge corpses and stalking a herd of triceratops, and they also encounter a giant flying reptile known as quetzalcoatlus. which stood taller than a giraffe and had the wingspan of a light aircraft.