Five years after their father killed their mother and abducted them, two young girls are found living alone in a long-forgotten forest cabin. Despite severe behavioural issues, including a fixation on their imaginary guardian "Mama", the sisters are sent to live with their uncle (Nikolaj Coster-Waldau) and his girlfriend (Jessica Chastain). Disturbingly, it seems that Mama has come too... Guided by chillmaster-producer Guillermo del Toro, first time director Andres Muschietti creates an eerily compelling ghost story with enough jolts and jitters to make the hairs on your neck not just stand up but fall out.
If the modern horror genre has taught us anything, it's that there's only one thing creepier than ghosts: orphans.
Combine the two and you're cackling like a maniac, as Mexican scaremonger Guillermo del Toro well knows after tingling spines with The Devil's Backbone and had everyone running from The Orphanage with the screaming ab-dabs.
Del Toro continues his campaign of orphanophobic terror as exec producer of this superior ghost opera, directed and adapted from his own short by Andres Muschietti, alongside his co-writer-wife Barbara and Neil Cross, creator of TV's Luther and veteran of, appropriately enough, Spooks.
It all begins when the stock market crash in 2008 prompts a desperate banker (Game of Thrones villain Coster-Waldau) to kill two colleagues and his wife before absconding with his two young daughters.
Five years later, the killer's brother Luke (Coster-Waldau again) is about to give up the search when the girls are miraculously found living like animals in a cabin deep in the Virginia backwoods.
Under the supervision of eminent psychiatrist Dr Dreyfuss (Daniel Kash), little Lilly (the impressively spooky Isabelle Nelisse) and her sister Victoria (Megan Charpentier) are released into the care of Luke and his Goth musician girlfriend Annabel (Chastain, enjoying the change from the serious stuff with black bob and full sleeve tattoos).
Even with the palatial home and funding provided by Dreyfuss, how a penniless illustrator and a child-resistant rock chick end up with guardianship over two psychologically unpredictable under-nines is a mystery. But it's nothing compared to the mystery of how the girls survived.
All Victoria can tell them is that they have been cared for by an entity called "Mama". And, as becomes freakily and frighteningly clear, Mama is not about to let their custody go uncontested.
However, despite opening with a bold move - revealing Mama as a genuine wraith - and sustaining a consistently eerie atmosphere, the film sticks rather too often to horror movie conventions.
Thus we are plunged into a world of cliches (dark spots spreading over walls, underlit rooms, people needlessly going places they shouldn't in the dead of night), illogicalities (the custodial matter mentioned above; the apparently hardcore muso Annabel never putting any music on) and unexplained plot threads (what's with the cherries and moths?).
Further sapping the scares, to get where it's going, the story keeps cutting away from Annabel's jeebies to labour through a convergent and overly familiar plotline involving a terrible yet unconvincingly forgotten piece of local history.
With Luke quickly sidelined, most of the fun and games come from seeing (and hearing) Mama put the wind up Annabel. It's here that the film is most effective; one scene showing Lilly at play through a half-open door is particularly well done.
Which just goes to prove that if children should be seen and not heard, the reverse applies to Mama.
Eliciting regular bursts of goosebumps and making sly nods to The Shining and The Exorcist, it's clear that the Muschiettis and Cross have done their homework.