'Walking Dead' marches into Season 6

There’s no rest for The Walking Dead’s weary.

After last season closed with an agitated Rick Grimes (Andrew Lincoln) killing a resident of the walled Alexandria Safe Zone, his band of survivors and the domesticated Alexandria residents regroup to face a giant zombie threat in the 90-minute Season 6 premiere (AMC, Sunday, 9 p.m. ET/PT).

“It’s one great beast that we have to wrangle, which I thought was a unique, brilliant way to start the season,” says Lincoln, whose Rick still bears the cuts and bandages from his Season 5 tangle.

Old foes, new threats power Season 6 of 'Walking Dead'

Zombie walkers — more than 600 in Sunday's episode, a record  —  are only one challenge. Vicious human Wolves roam outside Alexandria’s walls; inside, Rick’s temporarily settled road warriors navigate an uneasy relationship with the softer permanent population. Rick also must work through differences with longtime loyalists and deal with new arrival Morgan (Lennie James), a man he befriended in the show's pilot.

“We have groups of people that have transformed at different rates with different ways of surviving, all in the same place,” says executive producer Robert Kirkman, who created the comics series that spawned cable TV's top-rated show. “The people of Alexandria aren’t quite as prepared for this world as Rick and his crew are. We also have Wolves, who are perhaps closer to Rick’s group than they are to the people of Alexandria, but have a much more savage way of life.”

Expect more flashbacks this season. The premiere features two timelines, one in black and white that picks up immediately after the end of Season 5 and one in color that follows Rick & Co. as they prepare for a huge walker onslaught a few days later.

Rick’s group, often splintered, will band together this season, and Alexandria will remain “a pretty integral part of the show for the foreseeable future,” says Kirkman.

Characters from the comics, including Heath (Corey Hawkins) and Dr. Denise Cloyd (Merritt Wever), will be introduced in the series, which will feature many parallels with the comics.

“Season 6 has a vast amount of big moments pulled from the comics,” Kirkman says. “The two are very closely tied at this point.”

Dead averaged 20.1 million viewers last season, ranking as TV’s top show among young adults, so Kirkman sees no end in sight for the show, which spawned a Fear the Walking Dead spinoff.  Kirkman says he's "optimistic we will get to tell this long, sprawling, apocalyptic story until its natural conclusion. ... I definitely have an end game, but it’s something that’s very far off.”