True Blood's vampires have sex. Twilight's brood about not having it - which for their fans, of course, is an integral part of their appeal.

Meyer's hero, Edward Cullen (Robert Pattinson), is a gentleman vampire. Having been brought up on animal blood, he's sworn off the human kind.

He and his mortal girlfriend, Bella Swan (Kristen Stewart), now dare to kiss but whenever they do, Edward quivers delicately, preserving the possibility that the smooch could suddenly deepen into a love bite.

New Moon finds Edward and Bella settling into life as high school sweethearts in Forks, Washington, although she's already worrying about future complications.

She wakes on her 18th birthday from a dream in which she has turned into her grandmother while 108-year-old Edward has remained his perennially youthful, undead self.

This scenario has become common. We've seen variations on the theme of time playing tricks in The Curious Case of Benjamin Button, The Time Traveller's Wife and Dorian Gray. Welcome to the Botox generation's nightmare.

But we're not far into the story before Edward and the rest of his family decide they must leave Forks.

Bella will not be going with them, he tells her. Instead, she will stay behind to subside into a chronic sulk.

This means no more than a slight adjustment to Stewart's performance, which is already arranged around her pronounced gift for slouching and mumbling, but the prospect of watching her carry a large chunk of the film without her co-star is far from enticing.