When Danish mining engineers discover the tail of a huge prehistoric monster deep in the Arctic ice, they ship it to Copenhagen for research. There, Professor Martens keeps the tail frozen in a large refrigerated room. But someone leaves the door open, and the tail starts to thaw ... and grow! In time, it spawns an entire monster, kills a lab assistant and escapes. Reptilicus soon terrorizes Copenhagen in a grisly rampage. General Grayson and the army hunt him down only to discover that their explosives will create hundreds of new creatures.