Connor's big mouth gets him kicked off the team, just as a new anomaly appears in the London Underground. A nest of spiders and a huge centipede have infested the tunnels. When Stephen gets bitten, the team have to go after the culprit to get a sample of its venom to find an antidote. Things get even stranger when Stephen starts raving about seeing Helen, Cutter's long lost wife. She says she can give them the truth, but only if Cutter is willing to follow her into the past.
- 10-Minute Retirement: Cutter fires Connor from the anomaly project after he leaks confidential info. He's brought back on when it's determined he's the only one who can help identify the creature that attacked Stephen.
- An Arm and a Leg: A spider at the beginning of the episode loses one of its legs when a subway passenger slams a door shut on it.
- Artistic License – Paleontology: Arthropleurids were probably not as aggressive as they were in the show, as they had no real enemies on land.
- Ascended to Carnivorism: The Arthropleura, apparently. While we never see it eating, it has a venomous bite similar to a predatory centipede.
- Big Creepy-Crawlies: The creatures in this episode consist of a horde of camel spider-esque arachnids and a millipede-like Arthropleura, all much larger than any modern arthropod.
- Bunny-Ears Lawyer: Exemplified with Conor: he may be a screw-up at times, but he's really knowledgeable about prehistoric life.
- Creepy Camel Spider: Among the creatures that come through the rift to the Carboniferous is a swarm of gigantic, highly aggressive solifugids. They're ostensibly based on fragmentary fossils interpreted as the remains of a giant spider that were later identified as an unrelated aquatic creature, but there's never been evidence that real solifuges ever got that big or that aggressive.
- Day Hurts Dark-Adjusted Eyes: The team uses flashlights to drive the spiders back through the anomaly.
- High-Voltage Death: How the Arthopleura meets its end.
- Mix-and-Match Critters: The "spiders", despite their appearance, aren't true spiders, and are more closely related to scorpions. It's specifically noted that instead of fangs, they possess pincers.
- Poisonous Person: The Arthropleura has a venomous bite. It kills a pest controller with it, and nearly kills Stephen.
- Schmuck Bait: Connor buys into a suspicious creature sighting posted on the internet after telling his tech-savvy best friends about his previous run-in the Gorgonopsid.
