In the dense, snowy expanses of Lapland, a group of Danish miners stumbles upon an extraordinary discovery while drilling deep underground—an ancient, frozen tail of a large reptilian creature. The geological team, led by Professor Martens and his assistant Svend, transport the specimen to Copenhagen for research. As the ice thaws, the tail begins to regenerate into a full-grown amphibious monster, endangering the city with its destructive nature. Scientists work frantically to figure out how to stop the relentless regeneration, while military forces prepare for an all-out confrontation with the giant beast.

With the creature now free, it unleashes havoc across Copenhagen, leaving destruction in its wake. Buildings collapse, fires rage, and citizens flee in terror as the monstrous terror continues its rampage. As the authorities grapple with the chaos and scientists race against time to find a solution, a sense of doom pervades the city. The final battle looms as the only hope lies in overcoming scientific limitations and finding the creature's essential vulnerability to subdue it before it lays waste to all of Denmark.