Nick Cutter, Evolutionary Zoologist, finds himself confronted with the subject of his studies in a way he could never have imagined. Prompted by the enthusiasm of his graduate student Connor Temple, Cutter and lab technician Stephen Hart go to investigate strange animal sightings in the Forest of Dean. Close by, Abby Maitland, a zoo animal handler, is discovering the forest is home to a very strange pet. Could a lizard picked up by a young boy be an entirely new species?

Claudia Brown, Civil Servant, hopes Cutter will dismiss the sightings. However, he's reluctant to oblige. There's more than professional intrigue behind his investigations; eight years ago his wife disappeared from the heart of the forest.

Cutter invites Claudia to join the search, and they find a petrified Abby face to face with Scutosaurus – a giant beast from the Permian Era of 250 million years ago. Abby's convinced the Scutosaurus is “pure veggie”, so what's behind the sickening sight of a dead cow hauled high into a tree?

The young boy's tales of a monster at his window confirm Cutter's worst fears. A savage Gorgonopsid – one of the most dangerous predators of the Permian Era – is on the loose. Only Stephen's bravery manages to stop the boy and his teacher becoming its next meal.

Where are these creatures coming from? The Scutosaurus leads the team to the answer: a shimmering in the air, a distortion in the light and suddenly the Scutosaurus disappears before them. A rip in time – an anomaly – that leads back to prehistoric times. Cutter is determined to make the trip through, convinced that the answer to his wife's disappearance could lie on the other side.