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Teaser for 'Doctor Who' spinoff 'Class' issues dire warnings

"I can't always be there when you need me," Peter Capaldi warns students in the series "Class." Plus, get a peek at the "Doctor Who" Christmas special.

Why should the Doctor have all the fun fighting alien monsters? In the new "Doctor Who" spinoff series "Class," there's no Time Lord hanging around to protect humans from Daleks, Cybermen, Blinking Angels and the usual monsters the Doctor has battled since the beginning of "Doctor Who."

In the teaser trailer, released by BBC America Friday at New York Comic Con, the Doctor (Peter Capaldi) explains that he can't be there every time we humans manage to get into trouble with aliens.

"I can travel through space and I can travel through time, but I can't always be there when you need me," the Doctor says. "Sometimes you have to take survival upon yourselves. What will you do when the shadows come, when you can't turn away from the darkness ahead?"

Coal Hill School, where "Class" takes place, was first mentioned in the earliest episodes of "Doctor Who" all the way back in 1963.

The main characters in "Class" include students Charlie (Greg Austin), April (Sophie Hopkins), Ram (Fady Elsayed) and Tanya (Vivian Oparah), as well as their physics teacher Miss Quill (Katherine Kelly), all of whom appear in the trailer. And yes, Capaldi will also be showing up as the Doctor on "Class" as well. "Class" will debut on BBC Three and BBC America in 2017.

Speaking of Capaldi, BBC America also released on Friday a behind-the-scenes look at this year's upcoming "Doctor Who" Christmas special featuring Capaldi as the Doctor and the comic book superhero Doctor Mysterio (Justin Chatwin) to help save New York City from an alien threat.

The hour-long holiday episode, called "The Return of Doctor Mysterio," will be written by Steven Moffat and broadcast on BBC One and BBC America on December 25.