The crew of an underwater mining facility in Caithness, Scotland in 2119 discover an alien craft in the ruins of a submerged town. They bring it aboard only to find it is missing one of its two power cells, and four symbols carved into the interior walls. The engines suddenly ignite, and Commander Moran is killed. Later, the crew finds two ghostly figures, Moran and an unidentified alien, roaming during the night cycle, soundlessly chanting before turning to attack the crew. The crew take shelter in the base's Faraday cage which the ghosts cannot enter.