WARNING: The following contains spoilers for the Doctor Who New Year's Day holiday special, "Revolution of the Daleks," which premiered Jan. 1 on BBC America.
In "Revolution of the Daleks," the Doctor found herself locked up in a cosmic prison for years. Thankfully, an old friend was able to break her out: Captain Jack Harkness. Harkness was an important character introduced in the early seasons of Doctor Who's modern revival. The character debuted alongside the Ninth and Tenth Doctors, and he last appeared on the series in David Tennant's farewell episode in 2010 -- that is, until Jack made his long-awaited return in the Season 12 episode "Fugitive of the Judoon."
Now, Jack returns once again to finally meet the Thirteenth Doctor and help her and her companions save the world from the Daleks, and when the character signs off at the episode's close, he teases a potentially huge Torchwood reunion.
In the New Year's Day holiday special, Jack Harkness finds the Doctor in prison, breaks her out, reunites her with her TARDIS and together, they fly to Earth to help Graham, Ryan and Yaz stave off a Dalek invasion. However, when the fighting is done and the Earth is saved, Jack disappears. Then, while in the TARDIS, the Doctor gets a call from Jack, who explains that he has just reconnected with another old friend.
"Sorry, lost track of time," Jack says. "Gwen Cooper sends her love by the way -- says she took out a Dalek with a moped and her son's boxing gloves. Anyway, I'm gonna stick around on Earth and catch up with her. I'll call you."
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While Jack Harkness debuted in Doctor Who, the character also starred in his very own spinoff series, Torchwood. Introduced on Doctor Who, the Torchwood Institute was a covert organization tasked with protecting the world from extraterrestrial threats. While Jack headlined the series, he was also accompanied by Gwen Cooper, who was played by Eve Myles. Together, Jack and Gwen were a fan-favorite duo, and they were the only two characters who appeared in all four seasons of Torchwood.
Jack and Gwen haven't been seen together since 2011, but now the characters have finally reunited in "Revolution of the Daleks." Sure, fans don't see Gwen in the episode and Jack's call is likely meant to be nothing more than a fun nod for Torchwood fans, but it also unmistakably opens the door for an actual return. Jack appeared in two Doctor Who episodes in less than a year, which means he could always return for another adventure in the series' upcoming thirteenth season. He himself said he would be on Earth for a while, which means he is just a call away.
"Revolution of the Daleks" stars Jodie Whittaker, Bradley Walsh, Mandip Gill, Tosin Cole, John Barrowman, Chris Noth, Harriet Walter and Nathan Stewart-Jarrett. The Doctor Who holiday special aired on BBC America on Friday, Jan. 1.