The end is nigh once more, but nuclear disaster won't be the only threat on the horizon in the sci-fi thriller's fourth season

The 100 first look: Clarke, Bellamy, new Grounder prepare for the apocalypse

The 100 type TV Show network The CW genre Sci-fi

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It’s the end of the world as they know it…again.

Clarke (Eliza Taylor) may have defeated the murderous artificial intelligence A.L.I.E. (Erica Cerra), but she’ll have a much tougher time facing the villain of season 4: Earth’s second, impending doomsday, one caused by power plants melting down around the world. The news naturally sends everyone into a tailspin.

“If you can’t stop the end of the world, how can you find hope?” showrunner Jason Rothenberg says. “Some people will cling to their loved ones, some people will fight to their last breath, and some people are just done fighting.”

Others will try to find someone to blame. Not only will Clarke clash with City of Light followers who preferred brainwashing to dying of radiation, she’ll also encounter Grounders like Ilian (new recurring cast member Chai Romruen, below), who faults the Sky People for bringing down the latest wave of technology and destruction in the first place.

Image zoom Diyah Pera/The CW

“He was forced to do some horrible things while being driven by A.L.I.E.,” Rothenberg explains. “He’s dedicated to making sure that never happens again.”

But even if Ilian’s right, how will any of them survive? The key may be to look past tribal politics once and for all — something Bellamy (Bob Morley) begins to understand after sister Octavia (Marie Avgeropoulos) leaves him behind. “It’s human nature to save our families, our friends first,” says Rothenberg, adding, “Can you take a little bit less for yourself in order to let somebody else have something?”

Either way, they’re going to need a bigger bomb shelter.

The 100 returns Feb. 1 at 9 p.m. ET on The CW.