Underworld follows the story of an immortal battle between the world of vampires and lycans (known in vernacular as werewolves.) The main character, Selene, is a vampire. As a Death Dealer, she hunts down and disposes of lycans. The reason for this centuries-old war is unknown, until Selene encounters a plot by the lycans to find a man -- a human named Michael Corvin. As she delves deeper into the mystery, she comes to learn that everything she was ever told was a lie, and that the reason for their war is far more sinister than she could have imagined.