The Walking Dead's Lauren Cohan stars as American nanny Greta who, escaping an abusive relationship, comes to the UK to take up a job offer to care for a young boy in a remote English village.
Arriving at the parents' isolated mansion, Greta realises that her wealthy employers might be a bit batty as their eight-year-old son, Brahms, is actually a life-sized doll that she is tasked with caring for as though he is real.
The Heelshires (Jim Norton and Diana Hardcastle) present Greta with a list of rules that she must follow to ensure that all Brahms' needs are taken into account.
As soon Greta agrees to take the job, the Heelshires declare they are going on holiday and leave the young American alone with the doll.
At first, she treats the whole thing as a joke, and an easy way to make money, but when she fails to follow the list of instructions increasingly weird things start happening (strange noises, footsteps outside her room, disappearing items of clothing and jewellery etc).
Her only human contact is with village grocer Malcolm (Rupert Evans), who makes regular deliveries to the house and takes an instant shine to Greta (because Lauren Cohan!).
He explains that the real Brahms died in a fire 20 years earlier and since then the elderly couple have only been able to process their loss through the doll.
Quite quickly, Greta convinces herself that the doll is actually alive, or possessed by a ghost, and even manages to prove it to Malcolm (thus also proving to herself that she's not going mad).
But then, whether out of fear of what she believes she has stumbled upon or genuine dedication to the doll-boy, Greta becomes as obsessed as the Heelshires were in following Brahms' rules.
If you can surrender yourself to the slow build-up - and the general creepiness of the doll - The Boy is a powerfully effective, and quite old school, horror flick as well as a surprisingly intelligent and novel psychological thriller.
Things start to go quite batshit crazy in the third act - after Greta's brutish ex-boyfriend (Ben Robson) makes an appearance - but the key thing, and quite a rarity in a lot of modern horror movies, is everything makes sense if you take a moment to think about it.
The film overdoes the "and she wakes up from her nightmare" gimmick a couple of times, but doesn't ladle on the cheap jumpscares that tend to plague the genre these days, instead relying primarily on the weird atmosphere that Stacey Menear's script and William Brent Bell's direction have crafted.
A movie where the less you know about the plot the better, for good measure, The Boy throws in some red herrings along the way, ultimately building up to a genuinely surprising, yet wholly logical, clever and satisfying, climax.