Trust no one on “Doctor Who” Season 9. In episode 7, it was revealed that Zygons had taken human form and it was nearly impossible to tell who was a human and who was a Zygon clone. Even Clara (Jenna Coleman) was revealed to be a Zygon copy, but the Doctor (Peter Capaldi) will have to figure out who is who in episode 8, titled “The Zygon Inversion.” According to the synopsis, it’ll be one of his most difficult challenges yet.

“Shapeshifting Zygons are everywhere in the UK, and there is no way of knowing who to trust,” the synopsis warns. “With UNIT neutralized, only the Doctor stands in their way.” The Doctor will have to figure out something, and it looks like Osgood (Ingrid Oliver) might not be much help. She has a something that could start a war.

In the trailer, Osgood and her Zygon clone introduce a new weapon: The Osgood Box. It isn’t clear what the box does, but the results could be deadly. “The Osgood Box could end the ceasefire,” one Osgood says.

“The Osgood Box could start the war,” the other Osgood adds.

Clara’s Zygon clone also seems to be quite dangerous in the promo video. She’ll be on a mission for the Osgood Box, but she’ll get some help first. “You are going to be the first to make the humans see,” she says as she creepily approaches a very scared man. It isn’t clear what she is doing, but it looks pretty spooky.

Watch the trailer for “Doctor Who” Season 9, episode 8 below:

The Doctor will have to stop all the Zygons. “But how do you stop a war?” the episode 8 synopsis asks. “And what can the Doctor do to save his friends?” With such an emphasis on consequences in episode 7 (to the point where a town was literally named Truth or Consequences), viewers have to wonder if there will be some deadly results in episode 8 that are irreversible.

“Doctor Who” Season 9, episode 8 airs Saturday at 9 p.m. EST on BBC America.