The team are sent to deal with a Columbian Mammoth rampaging on the M25, and attempt to save a trapped motorist before she frightens the Mammoth into attacking again. Meanwhile, Connor and Abby search for the missing Rex and Caroline, and Stephen reveals his alliance with Helen Cutter. Connor and Cutter spring their trap to find the traitor in the ARC, and Oliver Leek's true colours are exposed and the team race to track him down.

While Stephen deals with a Silurian Scorpion attacking a popular beach resort, the team are trapped in Leek's bunker with an army of creatures. When the creature army escape and run amok in the bunker, the team must both escape the overrun bunker with their lives and stop the creature army from escaping onto the modern world.