British Army radiation drills at a remote Scottish base attract a subterranean, radioactive entity of unknown nature that vanishes, leaving two severely radiation-burned soldiers... and a "bottomless" crack in the earth. Others who meet the thing in the night suffer likewise, and with increasing severity it seems to be able to "absorb" radiation from any source, growing bigger and bigger. What is it?? How do you destroy a thing that "feeds" on energy?