When a truce between the human and magical worlds are broken, the elfin Prince Nuada begins to gather an army of horrific and fantastical creatures to rise up from the underworld to lay waste to human race. Man's only hope is the Bureau for Paranormal Research and Defence, a team of mutant and alien beings led by the fearsome Hellboy, a huge demon summonded by the Nazis near the end of the Second World War, and raised by the Bureau. Along with the fiery Liz Sherman, the merman Abe Sapien, and Johann Krauss, a disembodied ectoplasmic spirit contained in a containment suit, Hellboy travels between Earth and the Underworld to fight the his fearsome opponents. But his phsyical battles are no match for his inner struggles, as he agonises over whether to remain the the human world or return to the world of the supernatural, leaving all he knows behind.