Three kids, Steve (Patrick Gibson), Darren (Ciaran Flynn) and Beth (Lauren Coe), are stuck in Saturday detention at McKinnon School with their teacher Mr. George (Brendan McCormack). An anomaly opens and Therocephalians from the Permian and Triassic period come through. When Mr. George goes to the vending machine he is attacked and killed by a Therocephalian.
Jess (Ruth Kearney) alerts the team of the anomaly opening up. Becker (Ben Mansfield), Matt (Ciaran McMenamin) and Connor (Andrew Lee Potts) respond.
Back in the classroom, Beth insults the two boys and heads to the gym. When she leaves her phone behind Steve and Darren decide to teach her a lesson. They head to the schools CCTV room to upload an embarrassing video to the school. While they are there, they see Becker, Matt and Conner enter the school on one of the school’s security monitors. Thinking they are the cops the boys lockdown the school. The ARC team can’t get to the anomaly to lock it. The result is that dozens of Therocephalians come through and roam the hallways of the school.
At ARC, Phillip Burton (Alexander Siddig) tells Abby (Hannah Sperrritt) that they need to destroy all the creatures that couldn’t be sent back to their respective time, including Rex.
Episode 4 of season 4 features Therocephalians. Therocephalians were venomous, carnivorous quadrupedal mammal-like reptiles from the Permian and Triassic period. It is the first creature to kill a child in the Primeval series.
The Black Boxes were electronic recording and communication devices that team members wore, usually in conjunction with an earpiece. Named after flight recorders, the device could be clipped to the team member’s belt or something similar. They worked worldwide to track and communicate with and between filed personnel but would not work if the team member went through an anomaly or if manually turned off.