In ancient times, humans warred with magical creatures. In an effort to stop the bloodshed, King Balor of the Elves commissioned goblins to create a powerful Golden Army, mechanical soldiers that could decimate whole armies. Horrified by their destructive capability after a fierce battle, King Balor ordered a truce and divided the crown controlling the army into three pieces. One was given to humanity, and the others were kept by the magical world.

Centuries later, the truce is broken when Prince Nuada, Balor's son, defies his father's wishes and seeks to reawaken the Golden Army to eradicate mankind. In pursuit of the pieces of the crown, Nuada disrupts an auction and sets his sights on an unsuspecting Earth. Standing in his way is Hellboy, a demon raised by humans to protect them from supernatural threats. Alongside his pyrokinetic girlfriend, Liz, and aquatic empath Abe Sapien, Hellboy fights to protect humanity from this new menace. With the Bureau for Paranormal Research and Defense (B.P.R.D.) behind them, these unconventional heroes confront a host of fantastical creatures and navigate through a hidden magical realm that exists alongside the human world, attempting to thwart Nuada before his quest for the crown pieces is complete.