Primeval - Season 2 Episode 4 Underwater Menace

When a boy's disappearance down a drain coincides with an underwater Anomaly, Stephen and the ARC search the local canal for the aquatic predator behind the disappearance, while Cutter is convinced the creature is somewhere else. Cutter turns out to be right in the worst possible way when Abby is taken by Mer Creatures from the future and held captive in a flooded warehouse cellar. Meanwhile, Cutter and Connor learn that there is a conspiracy within the ARC.