'The Walking Dead' season 6 episode 2 spoilers: Who blew the horn -- the Wolves or a new villain?

AMC's "The Walking Dead" returned on Monday with an episode that saw Rick and the Alexandrians working out a plan to prevent a horde of walkers trapped in a quarry from becoming a threat to their lives in Alexandria Safe-Zone.

However, Rick's plan backfires, and it looks like Alexandria Safe-Zone is in a bigger trouble, which will be explored in detail in the upcoming episode of "The Walking Dead" titled "JSS". The official synopsis of the episode doesn't give away much other than to say that "a new problem arises for the Alexandrians," and one can safely assume that the walkers are going to wreak havoc as they try to enter the Safe-Zone.

Who could have blown the horn that's drawing the walkers to Alexandria Safe-Zone? One theory floating around suggests that it could be a rogue member of the Alexandria Safe-Zone community, who blew the horn to voice his dissent. However, it seems unlikely that someone in the community would put the entire Safe-Zone in danger.

The horn blow could also have been a cry for help from Alexandria.

Wolves are the next likely possibility. At the end of season 5, it was hinted that the Wolves will become a bigger threat to Rick and gang, and it looks like the time has come for the Alexandrians to face the next big villain.

So who exactly are the Wolves? They are a group of hostile survivors who lure and kill other survivors after taking all their supplies. They are known for carving "W" on the heads of the victims and using them as bait when they turn into walkers.

Elaborating on who the Wolves are, executive producer Greg Nicotero told Melty that they are known for "utilizing the people that they kill as ammunition to build a zombie army."

"We see them in Episode 9, when they get to Noah's neighborhood, and we see the 'Wolves Not Far' in the background. And when the W man says in the beginning [of Episode 16, to Morgan] 'we're going to take you too but you're not exactly going to be alive,' we realize through the course of the episode that they are setting booby traps everywhere so that they can take people's possessions and then use them as a means to build the walkers in the traps. So it's kind of a diabolical plan," Nicotero told Melty.

 "The Walking Dead" is aired at 9 pm on Sundays on AMC.