Abby (Hannah Spearritt) and Connor (Andrew Lee Potts) have been in the Cretaceous period for a year. In that time the headquarters of ARC has moved, and some new people have been hired. James (Ben Miller) and Becker (Ben Mansfield) are still there but Sarah (Laila Rouass) was killed on a mission. New on board are Matt (Ciaran McMenamin), the new team leader, and Jess (Ruth Kearney), team coordinator.
After being chased by a Spinosaurus, Abby and Connor need to move to a safer location. Connor finds, in the nest of a Raptor, the anomaly creator that Helen (Juliet Aubrey) lost before she went into an anomaly to Pliocene Africa. Connor manages to get the device to work, and they open an anomaly back to present time. Rushing to the location, Becker arrives shortly after they come through and the anomaly is locked. When Connor tries to close the anomaly with Helen’s device it has the opposite effect. The anomaly opens and a Spinosaurus comes through.
Episode 1 of season 4 features Raptors, Dracorex, a Cretaceous Fish, and Spinosaurus. The Spinosaurus was a giant theropod from the Cretaceous period. It is believed to be the largest terrestrial carnivore in history.
The 13 remaining episodes that comprised series 4 and 5 were originally intended to be one 13 episode run as series 4. They were mostly shot in Ireland. The city wall map in the office in Series 4 and 5 is Dublin City, turned upside down.
The Electro Muscular Disruption Weapons or EMDs were an advanced type of nonlethal taser gun designed by Matt to bring down creatures. There were several settings on the device based on the size of the creature. It is believed that the weapon was based on future technology that Matt brought with him to the present.