Cutter starts to suspect that his missing wife, Helen, knew about the anomaly. While everyone presumes the discovery of her camera—millions of years in the past—confirms her death, Cutter isn’t so sure …

Lester grows increasingly skeptical of “loose cannon” Cutter, but Claudia defends him as their only expert. Emotions are running high, and everyone is a little hot under the collar. While Lester suspects Claudia has ulterior motives for keeping Cutter on board, Abby hopes that Stephen might start to see her as more than just the “lizard girl.”

Meanwhile as Connor is spectacularly failing to woo Abby with camp-side tales, creatures invade the London Underground. In the labyrinth of tunnels, SAS soldiers come under attack from giant spiders.

When Cutter and his team head down to investigate, they find something far more ferocious waiting for them: Arthropleura, a slithering, 15-foot, vicious ancestor of the millipede. Stephen and Abby escape, but Cutter gets lost in a maze of underground passages. In the darkness, he sees a fleeting glimpse of a woman. Could it be Helen?

Stephen makes a desperate attempt to rescue Cutter from the fangs of the Arthropleura, but is attacked himself. In his poison-induced delirium, he thinks he sees Helen, and she has a message for Cutter.

Stephen’s only chance for survival is anti-venom. They know the only way to find a match is to get a sample from the creature. Connor uses his encyclopedic knowledge of all things prehistoric to guide the team to the creature’s lair, but can they get there in time to save Stephen? And will getting what they need cost another life?