‘Walking Dead’ ‘Killer Within’ Spoilers

It turns out the prison isn’t as safe as everyone thinks it is on AMC’s The Walking Dead.

If you thought the bloody season three premiere marked the end of Rick (Andrew Lincoln) and his gang of survivors going head-to-head against walkers for the immediate future, you’re sorely mistaken.

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While last week’s Woodbury-focused episode centered on the Governor, it doesn’t appear that Rick, Lori (Sarah Wayne Callies), Daryl (Norman Reedus), Glenn (Steven Yeun) did an ample job of securing the prison.

In three exclusive images from Sunday’s “Killer Within” episode, the group is tasked with going back to work to clear the area from a walker attack within the confines of the prison.

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With the group severed — Rick, Daryl and Glenn appear to be inspecting the grounds — how will the rest of the survivors fare from what appears to be an epic attack? Whose lives are in danger? And more importantly: Where did the walkers suddenly come from?

Check out the exclusive images above and below and hit the comments with your theories. The Walking Dead airs Sundays at 9 p.m. on AMC.