Hellboy, a bloodred, cloven-hoofed demon raised by the United States government, is a top field agent for the Bureau for Paranormal Research and Defense. He questions the unknown — then beats it into submission.

In the upper reaches of the Himalayas, Hellboy's ex-girlfriend, archaeologist Anastasia Bransfield, believes she has found the location of the legendary "Dragon King Pool" — thought to be the ancient dwelling of an evil dragon who inflicted horrific devastation on the land and its people. Every year the villagers would sacrifice a child to placate the beast, until one day an unlikely hero fought the dragon and won, bringing peace and prosperity to the land.

But Anastasia's triumph at her discovery is short-lived. Soon unearthly creatures are seen lurking around the dig site, someone is sabotaging the excavation with dire results, and the young daughter of one of the dig leaders goes missing. It looks like a job for Hellboy — but his toughest challenge might be putting his past with Anastasia behind him....