The key to enjoying Doomsday is to understand that it’s a mash-up. There’s some Michael Bay in there, some Fast and the Furious, even some Lord of the Rings. (Really.) But the influence that animates all these component parts is a deep and abiding homage to John Carpenter’s Escape from New York. It’s most noticeable, not in the plot itself (Carpenterian though it is), but in its execution. The plotting is pure freewheeling punk rock, the kind of thing you see from Carpenter when he trusts his vision to make The Crazy work. That’s Doomsday: A hilarious, brutal, crazy movie. It’s brilliantly stupid, or maybe stupidly brilliant. It’s Grindhouse without all the winking and nudging. It’s also a blast, and touches on a certain kind of greatness.

In brief: A plague (the “reaper” virus) has struck Scotland, and in a fit of Britishness, London walls the whole country off. The pitch is that the British government will go back in once things are settled, but naturally that doesn’t happen.

Until…

Until the Reaper virus shows up again smack dab in the middle of London twenty-some years later. What’s more: satellite imagery has picked up signs of survivors in Glasgow, people who are obviously immune to the virus, or have been cured. There’s a 48-hour window to retrieve the cure before the center of London will have to be sealed off. The order comes down to cycloptic badass Eden Sinclair (Rhona Mitra): Get in, find the rogue scientist Dr. Kane (Malcolm McDowell), get the cure, and get out again. By any means necessary.

Easier said than done. The interior of Scotland has gone completely Lord of the Flies. Punked-out savage cannibals rule the city, led by a deliriously homicidal maniac named Sol (Craig Conway). The countryside is dominated by for-real men and women in medieval clothing living in old Scottish castles. (I have a feeling that if I grew up in Scotland, I’d get a much bigger kick out of that.) Neither side is particularly welcoming to Eden and her ever-dwindling team, but that’s okay; she’s Snake Plissken with fewer one-liners. She’ll be fine.

And who knew Rhona Mitra could pull off this kind of role? Previously she’s only appeared in movies as “the hot girl” and on TV shows you couldn’t pay me to watch. She’s a good cipher and a convincing badass, and holding her own against Conway’s Sol is no small feat. The man is a pure hysterical nightmare; fun to watch, but not someone you’d want within 500 yards of anyone you love.

Maybe it’s a sign that I see too many grim, dour little movies, but Doomsday lit me up like no movie has in quite some time. It was just about the time Sol prances on stage in front of a screaming horde of his depraved followers to dance and sing and caper about like a lunatic that I started grinning.

The grin didn’t leave me; in fact, that grin only grew. Are they really doing this? I kept asking myself. And yeah: They were really doing that.  The punk savages roasting and eating one of Eden’s comrades? Why not. Faux medieval knights wearing smelted-metal armor? Sure! Increasingly spectacular car chase shot in the sun-bleached California tones of Fast and the Furious? Well, we have to get some exploding cars in here somehow…

It’s a kitchen-sink approach to filmmaking, which may explain a lot of the, er, confused reactions I’ve seen to the movie. It can be easy to see the patchwork lunacy and decide that what’s on screen is a starvation of imagination, laziness, or worse, a paint-by-numbers substitute for the actual act of creation. Me? I think it takes skill and a half to stir up the B-movie detritus of the past thirty years into something greater than the sum of its parts. Following the conventional, predictable beats everybody knows: That would be lazy, not to mention forgettable. Doomsday is neither.