It was Channel 4's biggest drama hit of the past 20 years. It was Digital Spy's no. 1 TV show of 2015. And it's coming back, back, BACK.

Humans is returning with more scintillating tales of sentient Synths – and here's absolutely everything we know about the eight new episodes.

Humans season 1 finale: How did it end?

Forgotten how things wrapped up? Here's a brief summary of what went down in August 2015's Humans finale...

Elster's children – with the help of Karen (Ruth Bradley) – succeeded in unlocking the secret to Synth consciousness, but before they could decide what to do with it, Niska (Emily Berrington) deleted the code from Mattie's laptop, storing what appeared to be the only copy on a flash drive.

In what appeared to be a big move towards establishing peaceful human/Synth relations, Niska entrusted the flash drive to Laura (Katherine Parkinson) – but Mattie (Lucy Carless) subsequently discovered that her spare flash drive was missing and Niska was later seen boarding a train, carrying said drive.

What actually occurred here isn't 100% clear. Did Niska leave Laura with a copy of the code, while also making a copy for herself? Or did she supply Laura with a dud and take the only real copy for herself?

The latter seems more likely, though you'd think that Laura or Mattie would have double-checked the data on their flash drive.

Humans season 2 cast: Who's in it?

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Practically the entire cast from the 2015 series will be returning for the next run. That includes...

The Hawkins Family: Katherine Parkinson as Laura Hawkins, Tom Goodman-Hill as Joe Hawkins, Lucy Carless as Mattie Hawkins, Theo Stevenson as Toby Hawkins and Pixie Davies as Sophie Hawkins.

The Synths: Gemma Chan as Mia, Colin Morgan as Leo Elster, Emily Berrington as Niska, Ruth Bradley as DS Karen Voss, Ivanno Jeremiah as Max and Will Tudor as Odi.

Odi's return might come as a surprise, given the character's apparent demise, but Will Tudor has confirmed he's back on the Humans set.

Plus: Neil Maskell will be returning as DS Pete Drummond, while so far unconfirmed are Jill Halfpenny as his wife Jill and Danny Webb as wicked Edwin Hobb.

Speaking of Hobb, Fred (Sope Dirisu) was also last seen powered down after being tinkered with by the mad professor - and it's unclear if he'll be revived.

One definite absentee from the roster is William Hurt, whose Dr George Millican met his end in the first series.

Real Humans – the Swedish drama which our Humans is based on – brought the character back as a "grief-bot" Synth, though writer Jonathan Brackley has suggested the UK series won't go down a similar path.

"We started quite close [to the Swedish show] and then it just organically grows away," explained writer Sam Vincent. "You make a small change and it's magnified further on down the path, so when it came to the second series, we knew it'd be an even bigger departure."

Daniel Zuchnik/WireImage/John Shearer/Getty Images/Gabriel Olsen

New cast members will include Carrie-Anne Moss – of Jessica Jones and The Matrix – as AI expert Dr Athena Morrow and Prison Break's Marshall Allman as Silicon Valley billionaire Milo Khoury.

Morrow is hoping to advance David Elster's work by creating a new kind of machine consciousness and is recruited by the young and ambitious Khoury.

Nashville's Sam Palladio is also on board as café owner Ed – and this trio will be joined by The Paradise's Sonya Cassidy (as Hester, a new Synth), Cucumber actress Letitia Wright (as a 'Synthie' - a human who mimics the androids) and Bella Dayne of Plebs (playing Astrid, who shares an important bond with Niska).

Humans season 2 spoilers: What's it about?

Reiner Bajo / Channel 4

Here's the official synopsis for 2016's episodes: "Niska is still at large and in possession of the consciousness code. Her synth family, Mia , Leo and Max, unaware of her location, are each trying to find their place in the world while Joe and Laura attempt to mend their marriage.

"As unconfirmed reports of synths behaving inexplicably surface, the ripple effects of one simple yet seismic decision sees the past return dramatically and surprisingly to the door of the Hawkins house. Joe, Laura and the entire family are faced with a difficult choice that will put the family under an intense spotlight.

Channel 4 / Colin Hutton / Kudos

"In the US, Milo Khoury, a young Silicon Valley billionaire, founder and CEO of a leading technology company is pioneering new research. But he needs help and attempts to recruit Dr Athena Morrow - the country's pre-eminent Artificial Intelligence expert.

"Suspicious of his motives and focussed on her own work Morrow is single-minded in her drive to create a new kind of machine consciousness.

"As an emerging form of intelligent life – the synths – and an established one – humanity – fight for their places in the world, a thrilling multi-stranded narrative evolves which continues to ask: who has the right to determine what it means to be alive?"

Colin Hutton / Channel 4

Oooh... but wait, there's more!

Series two will pick up "a few months" after the first, with the robotic Synths having "gone a bit deeper" into our culture. In short: they're no longer a novelty.

"Things are developing fast, as technology does in all areas," said head writer Vincent. "There's lots of new, society-wide effects which we're going to tell stories in."

The new characters played by Moss and Allman will "form part of what is a huge story", Tom Goodman-Hill told Digital Spy in April.

"It's much opened out from what we saw in series one," he hinted - with scenes set in Berlin, Bolivia, San Francisco and... erm... Margate.

The Hawkins family, meanwhile, are working to escape their troubled past - with Joe and Laura even seeing a Synth therapist for couples' counselling!

But the couple will find themselves at odds again over the notion of Synth civil rights: "What's particularly interesting about this series is that Laura was quite anti-Synth last series, and Joe was quite pro-Synth - in that he slept with one!" Parkinson said.

"And this series, very interestingly, it swaps and Laura becomes a champion of the Synths, of Synthetics having rights."

As for Palladio's Ed, he'll share most of his scenes with Gemma Chan's Mia, whose consciousness was restored in the first series.

Colin Hutton / Channel 4

"The story takes her down a very interesting path – needless to say it's quite an intense partnership for the two of them," the actor told DS in June.

"Their working relationship does develop and there are some huge moments that happen in our storyline which are really exciting to play."

"A bond definitely forms between them and it doesn't all go according to plan for her," Chan later told us. "She's still an innocent in terms of her knowledge of the outside world, and her experience with people, and she's really putting herself out there and it doesn't always work out for her."

Colin Hutton / Channel 4

We'll see more of a "progression" in Mia now that she's sentient full-time, too: "There are key moments in the series where you see her, for the first time, really make a decision...

"The stakes are really high, and things definitely don't go to plan. Mia has to respond, and I think you'll definitely get to see a much steelier side to her."

2016's episodes will also introduce a few new villains, though Vincent and co-writer Brackley wouldn't be drawn on whether volatile Niska will go over to the dark side.

Colin Hutton / Channel 4

"I think it's really tantalising and dangerous to put the future in the hands of one of your characters who's very unpredictable, volatile, and dangerous," Vincent said.

"We do have a new antagonistic force in mind for this show, which is going to come into play and be embodied by a couple of new characters, but I can't say any more than that."

Humans season 2 premiere: When's it back?

Series two started shooting in April, with new episodes scheduled to air on Channel 4 from Sunday, October 30 at 9pm and on AMC in February 2017.

Channel 4 began stealth advertising the new series in September, airing a mock PSA from fictional firm Persona Synthetics, urging viewers to return their malfunctioning Synths.

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Humans season 3: What's next for the Synths?

But is there a future for Humans beyond the next eight episodes? It seems there could well be, with writers Vincent and Brackley telling DS way back in October 2015 that the show "could run longer than two series".

"Definitely we have a very rough playful notion of what we'd do in series beyond two," said Vincent, adding that the show has "got a few series in it".

Meanwhile, Tom Goodman-Hill has hinted that some big changes could be heading the show's way if it were to continue into 2017.

Colin Hutton / Kudos / Channel 4

"I know Jon and Sam are already talking about what they want to do with the third series," he revealed. "Quite a lot of jaws hit the floor when they intimated what that was going to be!

"We know a little bit about that, which is very exciting – and beyond that, I don't know. I think it's the kind of story that has enormous potential to just run and run."

Katherine Parkinson has also suggested that Humans series 3 would be very different: "I know what I've shot and how that ends, and... it's really brave," she said.

"The way this series ends, the third series could end up being a whole different genre. It's very exciting."

"I feel like the way series two has been written is so that it can continue," insisted Theo Stevenson. "I feel like the sky's the limit with sci-fi series, but especially with Humans because as technology progresses, so can the series."

For his part, Sam Palladio has intimated that he's keen to come back for another go-around, saying: "I would hope that there may be a life for Ed in series three. I'd love to [come back]."

What does the future hold for Channel 4's Humans? Here's the latest on series 2 - and series 3

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