After a London Underground cleaner is fatally bitten by some type of giant insect, James Lester (Ben Miller) brings the team together to investigate. They find another anomaly that leads to the late Carboniferous, and a colony of giant arachnids that have come through. Using powerful lights to send the spiders back, the team are then attacked by the true killer, an Arthropleura, which bites and poisons Stephen Hart (James Murray). The race is now on to extract a sample of venom from the giant arthropod to synthesise an antivenom before Stephen dies.
