A below-average Joe drops by his ex-girlfriend's apartment just as a zombie virus breaks out in the German capital in "Rammbock," an effective slice of genre moviemaking on a budget.

Frosh helmer Marvin Kren and scribe Benjamin Hessler have clearly absorbed the conventions of the genre, from George Romero to "28 Weeks Later," but this compact Teuton take on two innocent strangers facing an undead apocalypse is singular enough to please more than just die-hard zombie fans. Ancillary pickups should turn its makers into names to watch.

Clueless Austrian Michael (Michael Fuith) still pines for his ex, Gabi (Anka Graczyk), and has come to Berlin to win her back, using the return of his keys to her apartment as an excuse. But instead of Gabi, he finds a cocky teenage plumber apprentice, Harper (Theo Trebs, "The White Ribbon"), in her digs. Before they've even exchanged two words, the unlikely duo is forced to barricade the door to keep out a horde of undead monsters. After spending the night together locked in Gabi's bedroom, they try to establish Gabi's whereabouts and if she's still alive. Radio and TV quickly fill in the flimsy zombie-virus back story.

The movie is billed as a "Kren and Hessler film," and per the press notes, the Austrian-born director and the German screenwriter watched Romero's 1968 classic "Night of the Living Dead" at an early and very impressionable age. The influence of that classic and countless others can be felt, though rather than simply aping rote genre conventions, the filmmakers have enough flair and talent to keep things fresh, even without much subtext.

One of the nicest touches is the film's setting: A rundown but typical Berliner Hof, a historical kind of apartment building with many floors, constructed around a courtyard. As in "Rear Window," the setting here is used to generate a sort of paranoid unease and creepy menace that quickly seeps into the pauses between the violent zombie attacks.

Kren is a precise director of action and actors, and Hessler not only has a strong ear for dialogue but also likes to toy with viewers' expectations. Pic inventively moves the characters from one apartment to the other as the protagonists attempt to stay one step ahead of the monsters.

By keeping them in or near the same building throughout, the makers respect the Aristotelian unities of time, place and action, which, together with the fast-paced editing and 60-minute running time, help this compact genre item pack a punch.