Lately, after watching movies like The Rezort and the trailer for the upcoming (as I write this) The Cured, I've been talking about how the zombie movement shows no signs of slowing down because of some very inventive takes on the genre and mythology.

With Earthling, the same could be said about alien invasions. Instead of the bombastic scope of Independence Day, the paranoid horror of The Thing or Invasion of the Body Snatchers or the freewheeling comedy of Edge of Tomorrow, this film feels and sounds more like a Sundance family drama that's all brown and grey tones and soft silences, and is far more about emotion than special effects.

Describing the set-up (aliens come to Earth as small slug-like animals that live in a lake, waiting to enter human hosts) makes it sound like an icky horror comedy, certainly not at home in a movie about a woman quietly having a nervous breakdown. But Earthling's biggest strength is how skillfully it handles two wildly distinct ideas – slimy creatures infecting brains and very grown-up emotional insight – and doesn't lose tone.

At least, I think that's what's going on. Judith (Rebecca Spence – cold, distraught and very human) is a teacher who it seems has lost a baby mid-term and has shut down emotionally as a result, cutting off even her understanding husband.

But there's a lot more to it, and as Judith wonders what's going on, so will you. It's got something to do with a satellite that's been approached by a strange object in orbit - in the beginning of the film, one of the astronauts aboard murders the rest of the crew when it comes aboard and is hospitalised in a coma when he returns to Earth. Judith starts to grow strange protuberances on her forehead. A new girl in her class, Abby (Amelia Turner) seems alternatively creepy, threatening and alluring, eventually approaching Judith to tell her she's one of 'them' – whoever they are.

It's not a spoiler to reveal that 'they' are the people who are either emissaries of the slug-animals in the lake or are being controlled/inhabited by them. Abby tries ever so gently to convince Judith of the truth about who they are, why they have these strange bumps under their hairline and why they feel such a kinship.

Again sounding much sillier on paper than it comes across in the film – where it's handled with gorgeous emotional nuance – Abby and her group of other enigmatic strangers (one of whom has been following Judith and spying on her) try to convince Judith they're all part of an alien race that's come to Earth and then forgotten their origins, the mysterious object approaching the spacecraft early in the film some kind of messenger reminding them to come home.

But in the ensuing years while they've been posing as human and inhabiting human bodies they've picked up human habits (like loving each other), enjoying the new experience so much they've forgotten what they truly are.

While she can't deny the connection she feels with Abby, Judith assumes they're all nuts – especially when their beliefs put them on course to doing something unspeakable to a child within their ranks. Meanwhile, the astronaut who survived the aftermath of the spiked object floating through space awakens, seemingly back to normal but far from it (this being a sci-fi story about aliens, after all), and he'll play a critical part in the plan the strange group has for its future.

The acting is suberb all round. You'll follow Judith's confusion and fear all the way, and as Abby, Amelia Turner is sublime, blending her sad, understanding eyes with a clear voice and an unshakable sense of being an ancient creature trapped in the body of a teenage girl.

Writer/director Clay Lifford also includes some scenes of true beauty that seem only to cement a mood rather than necessarily advance the plot. Shots of water vapor droplets drifting dreamlike in a void only further decouple the film from most movies of the genre.

Despite a lilting pace there are a lot of characters and a lot going on, but there's obviously an awful lot of skilled construction underneath not only to hold it all together but get all that storytelling across while retaining the sleepy, melancholy air.

To the extent there's a genre that mashes up creatures from outer space and damaged people learning to find beauty and connection in their hearts again, Earthling is the vanguard of the movement. Star-making for everyone involved.