Reality, to a chilling degree

The wonderfully, horribly scary movie “28 Days Later� induces the sort of physical reactions that these days are more often incited by the nightly news than the latest monster flick. You know the feeling -- the moist-slicked palms, the fast-thudding heart, the sense that being here (wherever you are) is an exceedingly bad idea and you need to leave right now. British director Danny Boyle knows that feeling too, which is why he’s filled his shrewd nightmare with rampaging zombies run amok in a world that from its fear to its follies looks an awful lot like ours.

It begins with an act of compassion -- a gesture of decency mixed with lamentable hubris. Somewhere in London, perhaps next week, perhaps next year, a group of masked animal-rights activists breaks into a laboratory stuffed with screeching chimpanzees. One animal rests on a table with his chest peeled open in a gruesome tableau while the others crash inside their glass cages in frantic isolation. The quietest chimp lies restrained on some kind of gurney, its head studded with electrodes and pointed at a bank of monitors flickering with violent imagery. We know these images not only because they’re the first things we see in the film, but also because this is the reality show that never ends -- the 24/7 human spectacle aflame with burning forests, burning cities, burning bodies and riots in the street.

The creature can’t look away; neither can we. Like Alex in “A Clockwork Orange,� forced to watch images of atrocities while listening to his beloved Beethoven during an experiment in psychosocial engineering, the chimp has to watch. But just keeping your eyes open can be lethal to the characters in this movie.

Within moments of the break-in, a scientist stumbles in on the interlopers. His voice rising to a hysterical pitch, he insists that the chimpanzees have been “infected� with virally transmittable rage and are highly infectious. The activists wave away the warning (no reason to believe the enemy, even when his voice quavers with terror) and open the cages. Instead of leaping into sheltering arms, the chimps go for the throat -- ripping into human flesh amid a volley of frenetically fast edits.

By tearing into their would-be liberators, the test animals throw the world into a catastrophic tailspin. What happens next makes for nerve-shredding entertainment, but because Boyle and screenwriter Alex Garland have more than scares up their sleeves, there’s more to “28 Days Later� than goose bumps. At once an old-fashioned freakout and an environmental cautionary tale (mess with Mother Nature and she’ll mess with you right back), the film combines two genre standbys -- lethal contagion and the undead -- and gives them a wicked, contemporary spin. Unlike the chimps, the humans can’t live with their rage. They thrash and shriek and spew fountains of blood. At some point, they also die (a temporary setback in a zombie movie), then rise again -- still shrieking, still spewing -- and begin taking everyone else with them.

When a bicycle messenger named Jim (an excellent Cillian Murphy) wakes from an accident-induced coma 28 days later, the world as he knows it is gone. Emerging naked from his hospital bed -- after that knockout first scene, Doyle has scared the pants off us, too -- Jim wanders the eerily quiet, depopulated London streets shouting desperate “hellos.� Because even post-apocalyptic stories need characters, he soon hooks up with a pair of fierce zombie fighters, the machete-wielding Selena (Naomie Harris) and her companion, Mark (Noah Huntley). In time, the survivors join forces with two others, Frank (the always-welcome Brendan Gleeson) and Hannah (Megan Burns), a father and teenage daughter graced with buckets of optimism and, almost as important, one of those sturdy London taxis parked in the garage.

For its first hour or so, “28 Days Later� is about as good as it gets, inside the horror genre and out. Working our nerves with appreciable glee, Doyle turns London into a disquietingly credible wasteland. The image of the big city as ghost town is a genre staple, but rarely has it been as effectively deployed as, in a terrific coup, Doyle and cinematographer Anthony Dod Mantle managed to shoot in London itself. When Jim first stumbles through the abandoned streets, he’s often seen in long shot, which allows us to soak in the reconfigured landscape -- the image of Big Ben towering over a London without traffic and tourists is one of the film’s milder shocks -- even as it replicates the vantage points of the city’s ubiquitous surveillance cameras.

Instead of trying to pawn off digital video as celluloid, Doyle embraces the medium and turns its limitations into a virtue. Like a postcard left in the rain, “28 Days Later� has the smudged look of degraded video, which dovetails with the overall unreality. Digital video doesn’t just add to the creepy sense that someone is always watching (but who?), it also allows Doyle to paint the sky a sickly yellow and transform panoramic London into a haunting charcoal cityscape. While there’s no denying his aesthetic ambitions, the director of slick entertainments such as “Trainspotting� isn’t the kind of filmmaker to undercut his basic commercial instincts. Digital video gives Doyle expressive range, and its jagged way of capturing motion means his zombies can run like crazy -- except that instead of batons, these sprinters are after meat.

Like many post-apocalyptic stories, “28 Days Later� loses steam in its final stretch. It appears there are a limited number of ways that the dystopian world can play out its closing chapter -- with another big bang or with a whimper. What happens after the bedraggled survivors leave London and its environs doesn’t have the pop punch of the film’s initial hour, its gallows humor or its moments of unexpected tenderness. Garland, who wrote the well-received novel “The Beach,� which Doyle turned into a big-budget dud with Leonardo DiCaprio, has a knack for intimate exchanges that oscillate between hectoring panic and giddy camaraderie. But for all its topical allusions to lethal viruses and environmental calamity, the screenplay ends up vague, unfocused.

Unlike George Romero, whose zombie masterpiece “Dawn of the Dead� earns a quick nod, Doyle and Garland aren’t at ease with pulp fiction or interested in mounting a political assault. These are savvy art-house lads, after all, which means they want to be taken seriously without risking offense. And, being lads, they can’t help but trot out some witless nonsense about man doing what comes natural -- grunt, grunt. Happily, this late spasm of macho doesn’t ruin the film’s pleasures, chief among them being the realization that movies still posse the power to scare us out of our minds. Boyle knows that the world is an unbelievably terrifying place, which is why even when zombies are rattling our cages and bringing down the house, he never takes us fully out of our reality -- he just throws open the door and watches us scramble.

*

‘28 Days Later’

MPAA rating: R, for strong violence and gore, language and nudity.

Times guidelines: Extreme zombie and human violence.

Cillian Murphy...Jim

Naomie Harris...Selena

Noah Huntley...Mark

Brendan Gleeson...Frank

Megan Burns...Hannah

Christopher Eccleston...Major Henry West

Fox Searchlight Pictures presents, in association with DNA Films and the Film Council, released by Fox Searchlight. Director Danny Boyle, writer Alex Garland, producer Andrew Macdonald, director of photography Anthony Dod Mantle, production designer Mark Tildesley, editor Chris Gill, music John Murphy, costume designer Rachel Fleming, makeup designer Sallie Jaye, line producer Robert How, Running time: 1 hour, 48 minutes.

In general release.