This third film in the Underworld series is actually a prequel, taking place during medieval times, way before the events of the first two films, showing how the Vampire/Lycan war got started.
This time, the plot revolves around the character of Lucian (Michael Sheen, reprising his role from part 1) the first werewolf who can shift between human and wolf at will. Essentially a slave to the Vampires, along with the other Lycans that he's been forced to create. He falls afoul of the tyranical Vampire leader Victor, who has him imprisoned after daring to go rogue and transform, even though he only did so to save Viktor's daughter from an attack by feral werewolves.
Notwithstanding, Lucian promptly triggers a revolt amongst his fellow Lycan slaves and having discovered he can also command the feral werewolves, enlists them to help attack the vampire castle, leading to a series of spectacular battles.
A number of actors from the previous fims return to reprise their characters, including Bill Nighy as Viktor, Steve Mackintosh as Tannis and Kevin Grevioux as Raze. Notably absent though is Kate Beckinsale as Selene, with this of course being set before her character was introduced to the series. However, Rhona Mitra, who plays Victors daughter and Lucians love interest Sonja, makes an excellent lead heroine for this third outing, who defies her Father and helps Lucian and the others gain their freedom.
If you've seen the other films, you'll know what to expect. Fans of the series should not be dissapointed, the film is very dark, very gothic and action packed, featuring plenty of fight scenes and lots of cool medieval weaponry. If you like gothic horrors or classic monster movies, then I heartily recommend this to you.