Plot
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, raises the child. Viktor kills Lucian's werewolf mother but envisions a race of lycan slaves for his clan that could keep guard during the day and be used as laborers by the vampires. As Lucian grows up, he and Viktor's young daughter Sonja (Rhona Mitra) develop an attraction that becomes love in their adult years, though they keep their relationship hidden.
Viktor has a relationship with the humans of the area; he protects them from the feral werewolves that roam the countryside in exchange for a tithe of silver and slaves. As human nobles meet with the vampire council for protection from the werewolves, Sonja guards them. Lucian hears werewolves near Sonja and orders Death Dealers to help her, but his orders are denied. He steals a horse and sword from a nearby Death Dealer and races to save Sonja. Werewolves attack and kill the nobles; Lucian arrives and when he changes into wolf form in order to protect Sonja, the werewolves back down. Viktor, despite acknowledging that Lucian saved his daughter, feels betrayed by his favorite pet and locks Lucian away after having him brutally whipped.
With the help of the scheming vampire Andreas Tanis (Steven Mackintosh), Sonja orchestrates Lucian's release in exchange for her seat on the vampire council. Lucian escapes, kills several of the vampires and begins liberating the other Lycans. The guards begin slaughtering the escapees. 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 laborers of the human nobles to their fight for freedom. He also travels to some caverns that are teeming with werewolves, attempting to bring them into the fight. The vampire nobles are outraged by the escape and growing chaos, demanding that Viktor recapture Lucian.
Lucian learns about Sonja's imprisonment and sets out to rescue her. 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.
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 werewolves, who attack the coven.
Lucian sees Viktor entering the fray and fights his way to him. 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 head and letting the body fall into the water below. Lucian emerges into 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. After this, Tanis is seen 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 (Shane Brolly) tells Selene (Kate Beckinsale) 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."
