In 1944, the Nazis build a dimensional portal off the coast of Scotland. With the help of Russian mystic Grigori Rasputin, they intend to free the Ogdru Jahad—monstrous entities imprisoned in another dimension—to aid them in defeating the Allies. Rasputin knows that this will be an apocalyptic event that he believes will create a paradise. He opens the portal with the aid of his disciples, Ilsa von Haupstein and Obersturmbannführer Karl Ruprecht Kroenen, member of the Thule Society and Adolf Hitler's top assassin. An Allied team is sent to destroy the portal, guided by young Trevor Bruttenholm, who is well-versed in the occult. The German team is killed and the portal is destroyed—in the process absorbing Rasputin—while Haupstein and Kroenen escape. The Allied team discovers that an infant demon with a right hand of stone came through the portal; they dub it "Hellboy".nnSixty years later, FBI agent John Myers is transferred to the Bureau of Paranormal Research and Defense (BPRD) at the request of Bruttenholm and he meets the adult Hellboy and a psychic, amphibious humanoid named Abe Sapien. He learns that a third BPRD member, Liz Sherman, has recently checked into a mental hospital to protect others from her volatile pyrokinetic abilities. Despite regular visits and coaxing from Hellboy, she is determined not to return. Kroenen and Haupstein resurrect Rasputin in the mountains of Moldova. The three unleash a hellhound known as Sammael. Rasputin imbues Sammael with the power to reincarnate and split his essence, causing two of the creature's eggs to hatch and mature each time one dies. Rasputin visits Liz as she sleeps, activating her powers and almost destroying the hospital. Myers convinces her to return to the Bureau.nnSammael's ability to multiply becomes a problem, as Hellboy repeatedly kills it, creating dozens. Abe is injured while retrieving some of its eggs, and Kroenen critically wounds one of the FBI agents sent with Hellboy. Kroenen, whose mutilated body is run by mechanical parts, shuts himself down, pretending to be defeated. Kroenen's body is brought to the bureau. FBI Director Tom Manning is angered by Hellboy's recklessness. Myers takes Liz out for coffee and to talk. Hellboy, jealous, covertly follows them. Rasputin appears at the bureau, reanimating Kroenen before confronting Professor Bruttenholm. Rasputin offers him a vision of the future, showing Hellboy is the agent that will destroy the world. Rasputin tells Bruttenholm he will also give him a quick death in return for the care he gave Hellboy. Bruttenholm is stabbed in the neck by Kroenen and dies clutching a rosary.nnManning takes over the B.P.R.D. and locates Rasputin's mausoleum in an old cemetery outside Moscow, Russia. A team led by Manning and Hellboy enter the mausoleum, but swiftly become separated. Hellboy and Manning find their way to Kroenen's lair and defeat him. Telling Manning to stay back, Hellboy reunites with Liz and Myers at Sammael's nest to defend them, but the creatures overwhelm him. Liz uses her pyrokinetic powers to incinerate the Sammaels and their eggs. Hellboy, Liz and Myers lose consciousness and are captured by Rasputin. To force Hellboy to release the Ogdru Jahad, Rasputin sucks Liz's soul out of her body, telling Hellboy that Liz will come back to life if he obeys. Hellboy awakens his true power as Anung un Rama, causing his horns to regrow. He nearly releases the Ogdru Jahad, but the injured Myers reminds him of who he is and that he has the right to choose his own path. Remembering his true self and what Bruttenholm brought him up to be, Hellboy breaks off his horns, returning to his former self and resealing the Ogdru Jahad. Hellboy stabs Rasputin with one of his broken horns.nnRasputin has been possessed by a creature from the Ogdru Jahad. The tentacled Behemoth bursts out of Rasputin's body and grows to immense size, killing Rasputin and Ilsa. Hellboy allows himself to be swallowed by the beast while detonating a belt of hand grenades. The explosion tears the Behemoth apart. Liz's vital signs are gone when Hellboy returns from the fight, but he whispers into her ear and her life is restored. When she asks how her soul was returned, Hellboy replies that he told the creatures from the other side the cost of taking her: "Hey, you on the other side. Let her go. Because for her I'll cross over, and then you'll be sorry." She and Hellboy kiss, and she surrounds them in flame as Myers stands and watches.