A mercenary reluctantly leads a motley crew of warriors who soon come to realize they've been captured and deposited on an alien planet by an unknown nemesis. With the exception of a peculiar physician, they are all cold-blooded killers, convicts, death squad members... hunters who have now become the hunted.
As the war between the vampires and the Lycans rages on, Selene, a former member of the Death Dealers (an elite vampire special forces unit that hunts werewolves), and Michael, the werewolf hybrid, work together in an effort to unlock the secrets of their respective bloodlines.
In the final days of World War II, the Nazis attempt to use black magic to aid their dying cause. The Allies raid the camp where the ceremony is taking place, but not before a demon - Hellboy - has already been conjured. Joining the Allied forces, Hellboy eventually grows to adulthood, serving the cause of good rather than evil.