We know about Eight and Eleven in Stranger Things – but what about 'Nine' and 'Ten'?
Now we've met Eight (Kali), could Eleven have other "siblings" from Hawkins Laboratory?
Since we first met the mysterious Eleven in Stranger Things, there has been one big unanswered question: if she's number 11, what happened to the other ten?
That's a question the Duffer brothers tackle head on in the first five minutes of Stranger Things 2 – but as a whole the season raises more questions than it answers.
As a gang of misfits try to outrun the police in a car chase through the streets of Chicago, the ringleader, a young woman called Kali, creates the illusion of a bridge collapsing to block their path. The police car skids to a halt, the illusion disappears and Kali drives on, blood trickling from one nostril. Tattooed on her arm is the number: "008"
So we now know Hawkins Lab has another alumna, this one with different "abilities". But Eleven's "sister" Kali (Danish actress Linnea Berthelsen) doesn't appear again until much later in season two.
When she does, we learn a lot of crucial information. Kali went "missing" when she was already a little girl, instead of being stolen as a baby like Eleven (real name Jane Ives). Then in Terry Ives' memories, we see Kali playing with Eleven in the Rainbow Room at the Lab.
She's a few years older than Eleven, which is why she remembers her "sister" while Eleven has forgotten the encounter. They must have been separated when Eleven was still quite young.
Now 'Kali' is hanging out with her gang in Chicago, tracing and killing everyone from the Lab in her quest for vengeance.
Where are Nine, Ten, and the rest of the child victims of Hawkins Laboratory?
If Kali is 008 and El is 011, that suggests there were two kids between them: 009 and 010. Kali is older than El (the original casting call was for actors between 30 and 38), so we'd be looking at two people in their mid to late teens.
And if their ages are so far apart, the first victim – 001 – could have been years and years ago. Is it possible that Eleven's mother Terry Ives could have been used in one of those early experiments? Perhaps that's part of why Dr Brenner stole her baby for further testing? We know she was involved in Brenner's mind control experiments while she was pregnant.
Neither Kali nor Eleven have mentioned any other kids they hung out with at the Lab. But it's entirely possible they were kept apart by "Papa" Brenner, completely unaware of each other's existence.
If other children survived their years at the Lab (and there's no guarantee that they did), there's going to be so much more story to tell in Stranger Things 3 and 4. What special abilities could they have? Where have their lives taken them since? And will they affect what happens in Hawkins?
Stranger Things 2 is available on Netflix now