The film tells the story of Lucian (Michael Sheen), the first werewolf able to take human form and to be called a Lycan. Viktor (Bill Nighy), a ruthless elder vampire, takes him home after killing his werewolf mother. Viktor envisions a race of werewolf slaves for his clan that could keep guard during the day and toil for the vampires. As Lucian grows up, he and Viktor's young daughter Sonja (Rhona Mitra) develop a mutual attraction that blossoms into love in their adult years, though they keep their relationship hidden from her father.
Viktor has a relationship with the humans of the area; he protects them from the werewolves that roam the countryside in exchange for a tithe. As human nobles meet with the vampire council for protection from the werewolves, Sonja guards them. Lucian hears the werewolves near Sonja and orders Death Dealers sent to help her. When his orders are denied, he steals a horse and sword from a nearby Death Dealer. Werewolves proceed to kill the nobles, causing Lucian to battle them. When Lucian changes into a Lycan in order to protect Sonja, the werewolves back down, leaving before Lucian is shot by Viktor's men. Viktor, despite acknowledging that Lucian saved his daughter, notes that Lucian transgressed the laws of the coven by removing the collar that keeps him in check (its inward-pointing silver spikes are designed to kill him if he changes into a Lycan) and feels betrayed by his favorite pet. He locks Lucian away after having him whipped.
With the help of the scheming vampire Andreas Tanis, Sonja orchestrates Lucian's release. In exchange, Sonja promises Tanis her seat on the vampire council. Lucian escapes, kills several of the vampires and begins liberating the other Lycans. The guards begin slaughtering the escaping Lycans. Sonja remains behind, but when Viktor discovers that she has had a forbidden relationship with Lucian, he imprisons her. Lucian and some of the freed Lycans roam the countryside recruiting many of the labourers of the human nobles to their fight for freedom from the nobles and the vampires. He also travels to a cavernous location that is teeming with werewolves, attempting to contact them. The vampire nobles are outraged by the escape and growing chaos, demanding that Viktor recapture Lucian. Viktor however, knows that Lucian will come to him.
Lucian learns about Sonja's imprisonment from one of her attendants and sets out to rescue her. Lucian orders his followers to wait, but be prepared to attack if he does not return. Lucian rescues Sonja from the fortress but they are attacked by the Death Dealers. Sonja confronts Viktor and tries to get him to call off his guards by revealing that she is pregnant with Lucian's child. Disgusted, Viktor overpowers her and imprisons both her and Lucian. Sonja is sentenced to death at a trial presided over by her father and the council. Lucian is forced to witness Sonja's death, in which she is burned to death by sunlight, passing out afterward.
Lucian awakens when Viktor comes in to view his deceased daughter. As Viktor removes the pendant necklace he gave Sonja, an enraged Lucian transforms and overpowers Viktor. Lucian takes Sonja's pendant, escaping out a window. The escape is stopped at the castle walls by Death Dealers who shoot Lucian with crossbows. With a thunderous howl, Lucian summons the freed Lycans and the werewolves, who attack the coven, overwhelming it. Viktor sends Tanis to remove the slumbering Amelia and Markus from their crypts before joining the battle with his personal guard. The council, meanwhile are overwhelmed and butchered by the rampaging werewolves.
Lucian awakens when Viktor comes in to view his deceased daughter. As Viktor removes the pendant necklace he gave Sonja, an enraged Lucian transforms and overpowers Viktor. Lucian takes Sonja's pendant, escaping out a window. The escape is stopped at the castle walls by Death Dealers who shoot Lucian with crossbows. With a thunderous howl, Lucian summons the freed Lycans and the werewolves, who attack the coven, overwhelming it. Viktor sends Tanis to remove the slumbering Amelia and Markus from their crypts before joining the battle with his personal guard. The council, meanwhile are overwhelmed and butchered by the rampaging werewolves.
Lucian sees Viktor entering the fray and fights his way to him. Viktor and Lucian battle their way to the catacombs. The fight continues until Lucian overcomes Viktor. Viktor's 'final' words attest to his regret at not having killed Lucian the moment he was born, to which Lucian sarcastically agrees before forcing his sword through Viktor's mouth and head and letting the body fall into the water below. Lucian emerges to the courtyard which is ringed with the surviving Lycans, werewolves and freed slaves. He declares this victory as only the beginning of what will become a war between the races. Tanis is leading a very alive Viktor into a hibernation chamber on a boat.
The film ends with the opening scene of the first Underworld, with the audio from the scene where Kraven tells Selene that it was Viktor who murdered her family, rather than the Lycans, and that Viktor spared her because she reminded him of the daughter he condemned to death; Selene replies to Kraven, "Lies!"
The film ends with the opening scene of the first Underworld, with the audio from the scene where Kraven tells Selene that it was Viktor who murdered her family, rather than the Lycans, and that Viktor spared her because she reminded him of the daughter he condemned to death; Selene replies to Kraven, "Lies!"
