People are disappearing without a trace around Blackwater Reservoir, leaving behind only empty boats, abandoned vehicles, and strange noises echoing from beneath the dark water. Called in under the cover of an environmental response unit, Inspector Marion Kenway and Zia Kose of the Pursuant discover that the threat isn't a natural creature. Deep beneath the reservoir lies a damaged portal from an ancient subterranean network, and a vicious, amphibious Level Two Uden feeding off its energy. To save the surrounding area, Kenway and Zia must battle the predator and seal the gate before more terrors escape.