Vampires are by nature cold-blooded creatures, and Tomas Alfredson’s “Let The Right One In” lowers the temperature further by being set in the wintry climes of Sweden. But paradoxically it also has a surprising degree of warmth in its story of a bullied young boy befriended by the perpetually twelve-year old girl vampire who moves in next door. This tale of an unlikely relationship between two misfits, shot through with splashes of poetic gore and imaginative twists on genre convention, is at once moody, evocative, chilly and surprisingly touching.

In 1982 Stockholm, thin, white-skinned, dour Oskar (Kare Hedebrant) lives with his divorced mother in a dingy apartment complex and is regularly taunted by classmates at school. Though he has occasional happy outings at his dad’s rural house, he’s obviously a troubled kid: he’s fascinated by news reports of crime and, when alone, fantasizes about taking vengeance on his tormentors.

He’s also intrigued by the people who move into the next flat, Hakan (Per Ragnar), a taciturn man who covers his windows with cardboard, and a strange girl named Eli (Lina Leandersson), who pops up, apparently unaffected by the frigid temperatures, at night in the courtyard where Oskar goes to be by himself. Though she solemnly informs the boy that she can’t be his friend, the two outsiders develop a bond of sorts. And her arrival coincides with an outbreak of murders in which the victims are drained of blood—the work of Hakan, whose job is to provide Eli with her needs. But his clumsiness at the task provides a dose of mordant humor even as his efforts are depicted in images that are both oddly beautiful and undeniably upsetting.

Hakan’s failure eventually takes the script, which John Ajvide Lindqvist fashioned from his own novel, into two overlapping threads: how Eli deals with getting nutrition on her own, and how Oskar confronts his demons. Ultimately the plot lines converge, in a couple of sequences that are brilliantly executed—one involving a curious neighbor who finds his way into Eli’s inner sanctum, and the other set in the school swimming pool, where Oskar’s enemies gang up on him. (Two more, centered on the neighbor’s girlfriend, use some of the established rules of vampirology to decidedly quirky effect, especially in the one where a bevy of cats show themselves as little feline versions of Professor Van Helsing.) The ending is satisfyingly unsettling.

This is an engrossing blend of suspense, horror and puppy-love story, carefully calibrated by Alfredson, elegantly designed by Eva Noren, and masterfully shot by Hoyte van Hoytema, who employs shots of falling snow as mesmerizing moments of pause between the deliberately paced scenes of human (and inhuman) interaction. The performances of Hedebrant and Leandersson are unerringly right, bringing texture to characters that could easily have come off as genre standards. The supporting cast bring authenticity to their parts, particularly the youngsters–Patrik Rydmark as Conny and Mikael Erhardsson as Martin–who play the schoolmates who make Oskar’s life a misery.

“Let the Right One In”—the title refers to the old bit of vampire lore that says the undead having to be invited to enter a home (something the film toys with at a couple of memorable moments)—is a moodily effective thriller that shows that there’s life in the undead yet.