The third installment of the saga about a centuries-old war between vampires and werewolves is actually a prequel that explains, insofar as that verb applies (which isn’t much), the origin of the conflict, which was only briefly covered in the initial film. But whatever the alleged rationale behind it—and as George Lucas conclusively demonstrated with the second “Star Wars” trilogy, there’s very little value in telling at length a story that everybody already knows in brief form—“Underworld: Rise of the Lycans” (the fancy word for werewolves) is every bit as inane and tedious as its predecessors, “Underworld” (2003) and “Underworld: Evolution” (2006). It’s not significantly worse, but then they set a very low bar. (And at little more than 80 minutes, not counting the final credits, it at least has the virtue of being significantly shorter than either of them.)

The two “heroic” characters from the preceding pictures, Kate Beckinsale’s vampire huntress Serena and Scott Speedman’s halfbreed Michael, are of course absent this time around, since the plot concerns events centuries earlier. It seems that the lycans (a human combination distinct from the purely animal wolves) were slaves to the vampires until they burst into rebellion under Lucian (Michael Sheen, reprising his role), the origin of the breed, against the bloodsuckers under nasty King Viktor (Bill Nighy, ditto).

Lucian’s always been loyal to Viktor, but things are complicated by the fact that he and Sonja (Rhona Mitra), the king’s headstrong daughter, are secret lovers—an interspecies affair that’s totally verboten, of course—and he even breaks the cardinal rule by transforming into his more hirsute form to save her during an attack. It all brings Viktor’s wrath upon them both, eventually prompting Lucian’s punishment—he’s savagely whipped not once but twice in the course of the film in scenes that rival “The Passion of the Christ”—and eventual rebellion.

The result is part ridiculous tragic romance and part ridiculous action flick, looking for all the world like another crappy video-game movie (a redundancy, perhaps) even though it isn’t actually one. Sheen (“Frost/Nixon”) and Nighy (“Valkyrie”) are both capable of good things, but under the direction of neophyte Patrick Tatopoulos (who designed the creature effects in the earlier movies) they indulge in grandiose, operatic overplaying that suggests they knew they were slumming and decided to give no quarter. Nonetheless neither they nor Mitra, who’s an almost perfect substitute for the almost-missing Beckinsale (who appears in a final shot at the close)—she scowls just about the same way and looks equally svelte in tight-fitting leather—do anything beyond filling the requirements of the very silly scenario. Nobody else is of much importance except for Steven Mackintosh as the duplicitous historian Tanis, who appeared in “Evolution,” and Kevin Grevioux as Raze, the black human with a basso profundo voice from the first picture, who comes off as a bargain-basement version of Michael Clarke Duncan.

“Rise of the Lycans” looks very much like its predecessors—no surprise there—which means that it’s all dank, shadowy Gothiness, with occasional shafts of shiny gray armor to add a brief hint of light. It’s not a very comfortable visual experience, but that was no problem for fans of the first two installments, and it probably won’t be in this case either.

To repeat the jibe that this franchise has invited from day one, for a movie about vampires and werewolves this one is both toothless and bloodless.