The opening credits play on a screen that churns and squirms with blood. But wait: there’s a hand, flexing. We’re inside a womb. And that’s a baby.

We can almost see it through the sheets of blood and the roiling amniotic fluid. Pregnancy is beautiful, sure. But it’s also scary, uncomfortable and very, very messy. Especially when a psychotic bitch in a gothic gown breaks into your home intent on cutting out your infant with a pair of kitchen scissors…

A home invasion movie made for €1.7m, Inside births unspeakable horrors from this devastatingly simple concept. It’s set over one unending night – Christmas Eve, the Paris riots raging beyond the edges of the frame – and pitches the widowed Sarah (Alysson Paradis) against a loopy, lupine-faced stranger credited only as La femme (Béatrice Dalle).

Dalle is exceptional. Dressed all in black like some High Priestess of Pain (or Betty Blue’s shadow, the insanity this time buzzing with evil), her eyes glitter out of the blackness and her gap-toothed smile flashes malice.

Paradis, meanwhile, makes for a resourceful, tough-as-talons heroine, yet her trauma’s palpable – so much so, Inside pulses with emotion despite being wall-to-wall in blood. Literally.

But this is a film that belongs to its tag-team directors, Julien Maury and Alexandre Bustillo. Describing their grisly debut as a “love story”, it’s clear that the real love here is in the filmmaking: the meticulously composed, artfully desaturated visuals; the thumping heartbeat of the electro score; the sudden aural assaults of tinnitus-thin ring noises; and the near-imperceptible use of smoke machines to bring the midnight-black shadows to shifting, seething life.

As with the Region 1 disc (Inside was released in France in 2007 and has been available on DVD in America since April 2008), the only extra here is the 52-minute doc, The Making Of Inside. It’s a belter though, bursting with gory details and refreshingly frank.

“They gave me lots of gifts, they told me I was beautiful, they posted me naked pictures of Colin Farrell,” says Dalle, explaining why she opted to work with a couple of no-name directors. She doesn’t appear to be joking. Paradis, however, needed no such persuading: the script was the best she’d read and she endured a month of training just so she could be beaten up convincingly on screen.

Inside isn’t flawless: it’s too bloody, almost farcically so, the mid-section playing like Home Alone rinsed in red. But it’s also chokingly suspenseful and ends with two of the most ghastly and moving images in modern horror.

That it deserves mention in the same gasping breath as fellow Gallic gut-churners Switchblade Romance and Martyrs confirms its position as one of the best horrors of recent years