The good friend I was seeing this movie with leaned over during the climax on the cliff top and said 'she looks like Corpse Bride'. It didn't exactly spoil it for me, but he was completely right, and it highlighted one of the film's few flaws – even though the monster had some very scary sequences, it was too CGI and in the end they wanted to show too much of it. That means it had to rely on jump scares for terror, and that both cheapens a movie and makes me like it less because of what a wimp I am.

But it's an effective horror movie, albeit with a template so many have followed before (three quarter mark detective work about insane asylum, believer who gets their ticket early, seeing the monster in the flash of a camera, etc). Still, writer/director Muschietti manages to get in some shots that prompt genuine dread and horror-movie amazement, like the child wheeling around near the roof of a room, laughing as if an adult is swinging her around even though the room's empty.

Another seamless aspect that's easy to miss because it's so well done is how amazing the little girls (Megan Charpentier as Victoria and Isabelle Nelisse as Lily) are in their roles as feral children slowly coming back to the world.

The girls are discovered in a remote cabin, having lived and survived there alone for several years after their father took them there to kill them and himself but was stopped by... something which dispatched him instead. When the girls' next of kin Uncle (Coster-Waldau) and his rocker girlfriend Annabel (Chastain) take them in, they're barely human, hiding under beds and snatching food scraps.

But something has followed them from the log cabin to the suburbs, and it's the reason they've survived by themselves for so long. Mama is a floaty-haired ghoul, the ghost of a nurse at a long-gone hospital who loved children, wanted one of her own, etc etc (you know the drill).

And Mama doesn't take kindly to the girls taking to a new mother – especially as Victoria's now old enough to realise she and her sister have to get with the real world, and that Annabel is their best chance.

Shepherded to the screen at the behest and backing of Guillermo Del Toro, it was a short film idea that's stretched a little beyond what a feature running time can manage without a few too many common tropes, but will you be scared? Until the climax that shows all too much, absolutely.