British filmmaker Neil Marshall earned a legion of new fans with 2005’s “The Descent,” a genuinely scary flick that put me, for one, off spelunking forever. And for his next act? An energetic but derivative apocalyptic adventure that Rogue Pictures has unceremoniously dumped into theaters without press screenings or even much promotion.

Being one of Hollywood’s Shameful Secrets™ (movies not screened for critics before they open) gives a film a certain stench, and it’s too bad that “Doomsday” is stuck with it. It’s not great — I’m not even sure I’d call it “good” — but the studios have certainly screened films that were worse. Heck, the studios have screened films that were worse this week (including one whose name rhymes with “Mever Mack Mown”). “Doomsday” is perfectly acceptable as a C+ movie, the kind that you don’t see on purpose but that will certainly amuse you if you happen to stumble into the theater accidentally.

It begins with florid narration by Malcolm McDowell, who tells us that a horrific virus — subtly called the Reaper Virus — wiped out much of England. Then a wall was built to divide the infected northern half of Britain from the clean southern half, and all the sick people up north were left to die in chaos. “Social order decayed along with the corpses,” McDowell says.

Now it’s 2035 and the virus has resurfaced in London. What’s more, the British government — led by a weaselly Scotsman named Canaris (David O’Hara) — spotted signs of life in the quarantine zone a few years ago, decades after the last remaining virus victims should have died. If there are survivors, that means they must have discovered a cure. And if they have a cure, we can break into the quarantine zone, take their cure, and bring it back to London.

It’s a huge leap in logic to say that if there are survivors up north then those people MUST have found a cure, but on such leaps are government policies determined. Canaris and his non-evil associate, Nelson (Bob Hoskins), decide to send a team in to bring back this alleged cure. (The government has a prime minister, too, but he doesn’t do anything.) The team is led by Eden Sinclair (Rhona Mitra), a cop/doctor/scientist (I was never really clear on what her job was) who lost her mom to the quarantine zone when Eden was a little girl and who now has a magical glass eye that can record video. That’s how you know it’s The Future!

Eden assembles a group of anonymous fellow cop/doctor/scientists, and off they go. The quarantine zone proves to have some society after all, but it’s the savage kind you see in “Road Warrior” and movies like it, the kind where people are cannibals and put on wild gladiator-style shows and wear bones in their hair. A character played by McDowell is there, and so is a crazy demigod leader named Sol (Craig Conway). Eden and her crew do battle with the locals; people are shot, stabbed, run over, and exploded; caches of weapons, vehicles, and cell phones are discovered (what luck!); and so it goes.

Marshall tends to film the fight scenes more confusingly than necessary, but his refusal to skimp on the blood and gore should make genre fans happy. He also stages a fantastic car chase sequence near the end (yes, even in wasteland of the future they can still have car chases), and he puts forth Rhona Mitra as a legitimately tough action heroine. Its occasional tense moments notwithstanding, it’s an action flick more than a horror movie. And as far as that goes, it’s not bad. Rogue Pictures might be ashamed of it, but there’s no need to be.

C+ (1 hr., 45 min.; R, lots of harsh profanity, a lot of fairly graphic violence, some brief nudity.)