An anomaly from a Precambrian period opens up on the fifteenth floor of a professional building. Out pours a fog comprised of sulfuric gas. In the fog are giant worms. Except for a few, the people in the building think it is a fire and most of them evacuate. The fire department is called. The team from ARC is called to investigate. Soon they find themselves prey for the giant worms.
Meanwhile, Nick (Douglas Henshall) convinces James (Ben Miller) to allow Connor (Andrew Lee Potts) to develop an anomaly detector based on radio waves. James allows Connor to work on the project but has him report to Oliver (Karl Theobald). Connor meets a young woman, Caroline (Naomi Bentley) at a music store. The two become attracted to each other. Abby, having grown fond of Connor, begins to feel tiny sparks of jealousy. Helen (Juliet Aubrey) injures herself in the past. She shows up in the present in Stephen’s (James Murray) apartment looking for help.
James has hired a new PR person to spin any problems stemming from creatures that come through anomalies. The new person is Jenny Lewis (Lucy Brown). Jenny is the spitting image of Nick’s lost love, Claudia. Nick becomes obsessed with Jenny and believes she is a different version of Claudia. Jenny gets a baptism of fire when she realizes that her job is to gaslight people that have seen prehistoric creatures.
Episode 2 of season 2 features Precambrian Worms. The worms are about six feet long with hair-like spines making them resemble sea cucumbers. They have a retractable proboscis that contains a tongue and teeth and are carnivorous. They spit a black viscous liquid from their mouths. The worms only breathe sulfuric gasses. They could live in the present because a sufficient enough of the atmosphere also came through the anomaly. When they came in contact with oxygen and heat, they would swell up and explode. Because they kept their young inside their bodies, they would expel their young when they exploded. They young would try to seek out a host to invade.
There is a Wilhelm scream when the janitor is killed by a worm.