Expect some familiar faces in “Doctor Who” Season 9, episode 7. The Zygons and Osgood (Ingrid Oliver) will return for the installment, titled “The Zygon Invasion.” According to the synopsis, the scientist will find herself in danger from which only the Doctor (Peter Capaldi) and Clara (Jenna Coleman) can save her.

“The Zygons, a race of shapeshifting aliens, have been living in secret among us on Earth, unknown and unseen -- until now!” the synopsis teases. The Zygons have appeared a few times in “Doctor Who,” most recently in the 50th anniversary special in 2013. In episode 7, they’ll make their return, but they aren’t all living peacefully among the humans.

“When Osgood is kidnapped by a rogue gang of Zygons, the Doctor, Clara and UNIT must scatter across the world in a bid to set her free,” the synopsis says. “But will they reach her in time, and can they stop an uprising before it’s too late?”

The Zygons have devised quite a plan, but how can they kidnap a dead girl? Osgood’s last appearance in Season 8 showed Missy (Michelle Gomez) vaporize her. It seemed Osgood was dead, but could she have survived? Fans will have to tune in on Halloween to see if the Doctor traveled to a time when Osgood was alive or if Missy actually spared her.

Watch the promo video for “Doctor Who” Season 9, episode 7 below:

As with every other episode in Season 9, “The Zygon Invasion” is a two-part story, so the Doctor might not save the world in one hour. The episode will be followed by “The Zygon Inversion” on Nov. 7.

“Doctor Who” Season 9, episode 7 airs Saturday at 9 p.m. EDT on BBC America.