Rachel Nichols stars in “Continuum”

The end of times: After a lot of traveling through both space and time, a beloved and critically acclaimed science fiction thriller is nearing its end.

"Continuum," the riveting adventure about a cop from the future fighting to stop a group of time-traveling rebels, premieres its fourth and final season Friday, Sept. 11, on Syfy.

Not only does the show's plot revolve around time travel, but the show itself has made quite the journey through space. The Canadian show, which is set in Vancouver, British Columbia, is filmed and produced in its home and native land, but it has been picked up in the U.S., the U.K. and even as far away as Australia.

This season starts not long after the events of the season 3 finale. The star of the show, American actress Rachel Nichols ("Alias," "Criminal Minds"), plays the tough-as-nails Kiera Cameron, a cop from the year 2077 who has been accidentally transported to the year 2012 with a rebel group called "Liber8" that she was trying to apprehend.

Now trapped in our present day, she teams up with the local police to try to apprehend the villainous members of Liber8 -- while also trying to conceal the fact that she's not from our time period.

Of course, Nichols is far from the only cast member. The stellar cast includes Victor Webster ("Bringing Down the House," 2003), Erik Knudsen ("Scott Pilgrim vs. the World," 2010), Stephen Lobo ("Smallville"), Roger Cross ("24") and Luvia Petersen ("The X Files: I Want to Believe," 2008).

Whether time itself has an end is a question that has intrigued philosophers for millennia, but this time-traveling thriller's timeline is running short. Fans of "Continuum" won't want to miss its final season when it premieres Friday, Sept. 11, on Syfy.

Maisie who?: "Doctor Who" is no stranger to playing games with its guest stars, but one upcoming visitor may just take the throne.

English actress Maisie Williams captured the audience's hearts with her portrayal of the tomboyish but emotionally scarred Arya Stark in HBO's runaway hit "Game of Thrones," a role that has really jump-started her career.

The 18-year-old actress will be guest starring alongside Peter Capaldi ("World War Z," 2013) in the upcoming ninth season of "Doctor Who," the jewel in BBC's crown. Season 9 premieres Saturday, Sept. 19, on BBC America.

The role she'll be playing has, so far, been a closely guarded enigma.

"She is a brand-new character. She is not someone from the Doctor's past," said "Doctor Who" showrunner Steven Moffat at the recent Television Critics Association summer press tour. "It's a significant role. We're not throwing her away."

Williams' star has certainly been rising since she first appeared in "Game of Thrones." She's been in "Heatstroke" (2013), "The Falling" (2014) and "Gold" (2014) on the big screen, and has had guest roles in the BBC's "The Secret of Crickley Hall" and as a voice actress in "Robot Chicken."

With "Game of Thrones'" continuing success and her character a fan favorite, it seems that Williams' acting career has taken off, and appearing in "Doctor Who" is unlikely to change that. The science fiction show's ninth season premieres Saturday, Sept. 19, on BBC America.

Born again: John Constantine may be down, but he's certainly not out. Last season's "Constantine," an NBC show about a demon hunter fighting the forces of darkness assaulting our world, was canceled after only a single season, but the show's star is returning to the role for a special guest appearance in another superhero adventure.

Matt Ryan ("Criminal Minds: Suspect Behavior") starred as "Constantine's" titular hero, and he'll be donning the character's iconic trench coat for an episode of the upcoming fourth season of "Arrow," which premieres Wednesday, Oct. 7, on CW.

Despite the two shows airing on competing networks, the crossover isn't as far-fetched as it may first appear. Both shows are produced by the same studio -- Warner Bros. Television -- and both Constantine and "Arrow's" Oliver Queen (Stephen Amell, "Heartland") are based on characters from the DC Comics universe.

During his appearance in "Arrow," Ryan's Constantine will come to the aid of the bow-wielding hero when his arrows just aren't enough to defeat a growing threat.

Ryan's return to his old character will no doubt fuel rumors that "Constantine" may one day rise, phoenix-like, from its grave. The show was canceled in May despite rumors of it moving to another channel, and at the time, "Arrow's" Amell offered on Twitter to appear as a guest star should the series be given another chance. For now, though, "Constantine" -- the show -- is very much dead. For one episode of "Arrow," at least, the character will get a chance to live again.

Season 4 of "Arrow" premieres Wednesday, Oct. 7, on CW.