Connor is picked up in a video store by a young woman called Caroline. Caroline is everything Connor is not; poised, well connected and effortlessly sexy, her interest in him is all the more surprising for it. But Connor isn't waiting around to analyse his good fortune. Unfortunately, his good luck is not appreciated by all: Abby and even Rex view Caroline as an irritance, though Abby's distaste for her may be more personal in nature. Though the pair have to leave to deal with an anomaly, to Connor's amazement, Caroline leaves him her phone number and asks him to call.
Meanwhile, Helen Cutter is traveling in the Cretaceous period, where she runs afoul of a Pteranadon. She is wounded and travels through an anomaly to Stephen's house for aid. However, he has to leave quickly with the rest of the team, and warns her to be gone by the time he gets back..A gleaming new skyscraper in the center of the city has quickly developed a reputation for teething problems in it's electronics, so no one is surprised when smoke is found creeping out from the server room. On inspection, a janitor finds a thick layer of mist hugging the floor and a foul sulphurous smell - but no fire. he also discovers an Anomaly inside a room, where the mist is coming from. Then a shadowy creature can be seen slithering by in the mist and the man suddenly loses his footing as something unseen attacks and drags him out of sight screaming as the mist continues to spread.
Cutter, meanwhile, is having to deal with the presence of Jenny Lewis, the team's newest recruit, a top-notch PR liaison and a complete doppelganger of Claudia Brown. Connor narrowly prevents Cutter from embarrassing himself by expounding on his belief in public, urging his professor not to continue until he can gain proof. Jenny, however, seems unperturbed by the team's eccentricity and unconvinced on the severity of their work. However, Cutter has other matters to attend to: he and Connor get down to the serious work of trying to build an anomaly detector system. For the first time since the crisis began the team will no longer be dependent on luck to find the anomalies. Lester is skeptical of the plan but Leek is enthusiastic and Lester reluctantly agrees to giving them a budget. Connor is immediately set to work.
Meanwhile at the skyscraper, panicking staff flee as the sinister mist oozes down the stairs and lift wells, accompanied by a foul stench of rotting matter, setting off the fire alarm. A fire crew arrive and enter an office waist high in sulphurous fog. They are attacked by shadowy, giant creatures; we see tantalising glimpses of these odd, frightening beasts that seem to live inside the mist. The skyscraper is evacuated but in one glass-walled meeting room a group of executives refuse to leave, as they are in a middle of an important video conference that will decide the future of their company. The man leading the company tells the Japanese businessman he is having the video conference with that the alarm is just a drill and continues with the meeting. They cannot yet see the mist enveloping them...
By the time the team arrive the skyscraper is filling with fog and a fireman has been horribly killed. While they explore offices full of abandoned chairs and desks they discover that there are giant carnivorous worms moving inside it. Leaping from desk to desk they only just manage to escape with their lives. Jenny, who has been appointed as operations manager on the ground (reporting directly to Leek and Lester) is given her first taste of her new job and nearly breaks down with terror when she realises what she is dealing with (after Cutter narrowly rescues her from one of the creatures). But she recovers, showing real guts in the process and Cutter cannot help being impressed, even though the two of them find themselves in almost constant opposition. Meanwhile, Cutter tasks Abby and Connor with obtaining equipment to clear fog: after Oliver Leek's tour of the armoury proves of little use, the pair decide to obtain leaf-blowers from a nearby garden centre. However, in the corridors of the ARC, Connor encounters a security guard who looks all-too-familiar. He's certain it is the cleaner who was injured by the infant Raptor previously but Abby is not convinced...
Meanwhile, the executives finally smell the sulphurous gas. One of them leaves to investigate, but much to the horror of his colleagues, a few moments later he is killed by the worms. The team and a fire woman find the executives. While trying to save them and evacuate them from the building, Connor nearly gets eaten by a giant worm. He and the rest of the crew are walking down the stairs when he says, "I think we're all right now." Then, a huge worm comes from the ceiling and swallows his head and Cutter, with a sabre that he snagged from a display, cuts the worm in half to save Connor. While washing the worm's saliva off, Connor accidentally washes Caroline's phone number off.
The race is on to rescue the executives in the meeting room before the worms get to them first. In the process, Stephen gets separated and gets trapped in a lift shaft. Cutter realises the worms can't survive outside the fog (as Pre-Cambrian creatures, the worms are more used to a sulphurous atmosphere, making oxygen poisonous to them) and Connor and Abby set about turning up the heating in the building. They succeed in doing this but no one is prepared for the effect the heat has on these deadly creatures - they explode, shooting their parasitic young all over the room. Cutter warns everyone not to let them break the skin, and after setting off the building's fire control system, the worms fall to the ground where they die.
In the end, back at Abby's flat, Caroline makes a reappearance, having conveniently left her phone behind. Unable to believe his luck again, Connor offers to take her out for a drink, which she accepts: they depart, leaving behind a jealous, scowling Abby. Elsewhere, Cutter is standing outside of Jenny's house: he knocks on the door, and offers to explain everything to her. But he is shocked when her fiance comes to the door. Making his excuses, he departs: unbeknowst to him, Helen is sitting in her car nearby, watching the discussion with a malicious smile on her lips...
- Douglas Henshall as Nick Cutter
- James Murray as Stephen Hart
- Andrew-Lee Potts as Connor Temple
- Hannah Spearritt as Abby Maitland
- Juliet Aubrey as Helen Cutter
- Ben Miller as James Lester
- Karl Theobald as Oliver Leek
- Lucy Brown as Claudia Brown/Jenny Lewis
- Naomi Bentley as Caroline Steel
- Tim Faraday as Security Guard
- Sidney Cole as Fire Chief
- Jason Thorpe as Terry
- Ruth Millar as Shelley Mitchell
- Shelley Minto as Firewoman Cooper
- Ged Simmons as Fireman Armstrong
- Rupert Young as Mike
- Togo Igawa as Mr. Nagata
- Helen Cutter
- Nick Cutter
- Jenny Lewis
- James Lester
- Oliver Leek
- Connor Temple
- Abby Maitland
- Stephen Hart
- Terry (only appearance)
- Shelley Mitchell (only appearance)
- Mr. Nagata (only appearance)
- Japanese Woman (only appearance)
- Fireman Armstrong (only appearance)
- Firewoman Cooper (only appearance)
- Caroline Steel (first appearance)
- Fire Chief (only appearance)
- The Cleaner
- Mike (only appearance)
- Janitor (only appearance)
- Claudia Brown (flashback, mentioned)
- Anomaly Research Centre
- Abby Maitland's flat
- Inner City Office Block (only appearance)
- Stephen Hart's flat (first appearance)
- Video store (only appearance)
- Jenny Lewis' flat (only appearance)
- Cretaceous desert (latest appearance)
Objects and technology
- Anomaly Detector (mentioned)
- The events at the end of Episode 2.1 were continued in a flashback as seen by Nick Cutter.
- References to Episode 2.1:
- In Episode 2.3, Connor builds an Anomaly detector as discussed in this episode.
- In Episode 2.4, Connor mentions that he had seen the Cleaner disguised as a soldier at the ARC.
- The Precambrian worms return briefly in Episode 5.5.
- Episode Guide on itv.com 
- ↑ http://www.bbcamerica.com/primeval/guide/season-2/episode-2/
- ↑ http://www.fernsehserien.de/primeval-rueckkehr-der-urzeitmonster/episodenguide/staffel-2/8020
|Episode 2.1 • Episode 2.2 • Episode 2.3 • Episode 2.4 • Episode 2.5 • Episode 2.6 • Episode 2.7|