The mythical world starts a rebellion against humanity in order to rule the Earth. Hellboy and his team returns and they must save the world from the mythical creatures. Now, as the creatures who inhabit the spiritual realm get ready for an all out attack on humans, the only one capable of saving the Earth is a tough-talking hellspawn rejected by both worlds.

In 1944 the Nazi military and scientific departments are researching the occult. Russian mystic Grigori Rasputin builds a dimensional portal off the coast of Scotland, where he intends to use it to bring about the destruction of Earth. In his employ is the ultra-silent assassin Karl Ruprecht Kroenen, who seemingly can't be killed. However, the United States has sent forces of their own to Scotland, along with Professor Trevor Bruttenholm, who is well-versed...