‘The 100’: Everything You Need to Know Before the Season 4 Premiere

It’s the end of the world as The 100 knows it.

The series began with the denizens of the Ark fleeing the dying space station for the now safe-from-radiation Earth. But in Season 4’s premiere, Earth itself is in peril — and humanity may have just six months left to live.

In last year’s Season 3 finale, Clarke (Eliza Taylor) saved everyone from the control of A.L.I.E., an artificial intelligence with nefarious purposes. But in the process, she learned that many of the planet’s remaining nuclear reactors were melting down. Now, Clarke has a seemingly impossible mission ahead — to unite everyone in the cause of survival.

It’s been a while since the events of last season, so here’s a guide to help you catch up on everything that Clarke, Sky Crew, and the Grounders faced.

The key

Season 3 began with the introduction of A.L.I.E., an artificial intelligence program who seduced Jaha with the vision of “The City of Light,” where people experience no pain or suffering. That turns out to be a virtual reality world, accessed by swallowing a “key” or chip. But anyone who takes the key becomes a tool of A.L.I.E. Jaha returns to Arkadia and begins to recruit followers, including Raven, Abigail, and Jasper.

Clarke rises

After a few months of living in the wilderness alone, Clarke is kidnapped by a bounty hunter who turns out to be Prince Roan of Ice Nation. He delivers her to Lexa, whose purpose is to initiate Sky Crew into her coalition. When war breaks out between Sky Crew and the Grounders, Lexa’s adviser attempts to shoot Clarke — but ends up killing Lexa instead, triggering a succession crisis.

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Grounders vs. Sky Crew

Arkadia discovers that members of Farm Station, including Monty’s mother and leader Pike, survived the descent to Earth. But most of them are killed when Ice Nation blows up Mount Weather. Vowing revenge, Pike wins the election for Chancellor, then recruits Bellamy and Monty and other soldiers to attack an army of Grounders. Kane attempts to make peace by giving Pike to the Grounders, but the plan fails and Kane is sentenced to execution. Bellamy rethinks his allegiances and works with Octavia to rescue Kane, as well as Lincoln and other Grounders imprisoned in Arkadia. But while Kane escapes, Lincoln is shot in the head by Pike. Later, Bellamy turns on Pike completely and gives him to the Grounders.

The Flame

With Lexa dead, the Grounders must choose a new Commander. But Ontari, an Ice Nation bodyguard, wipes out the other candidates. Titus entrusts Clarke with “the Flame,” which turns out to be a chip much like A.L.I.E. It turns out to be A.L.I.E. 2.0 and has been passed down through the generations in each new Commander. Clarke attempts to get the Flame to Luna, a candidate who was a friend of Lincoln’s. But when that mission fails, it falls to Clarke to take in the Flame, temporarily, to save everyone from A.L.I.E.

The resistance

The numbers of A.L.I.E. zombies increased, with Jasper becoming one of them. Raven, meanwhile, is kidnapped by Monty, who plans to use an EMP to destroy her chip. But in his quest, he is forced to shoot and kill his chipped mother. Raven reveals that the 2.0 chip is the only thing that can fight against A.L.I.E.

The City of Light

Jaha is able to convert not only Sky Crew to A.L.I.E., but Ontari and the Grounders as well. Clarke teams up with Raven, who figures out a way to hack into A.L.I.E.’s code. The initial plan to give Ontari the 2.0 chip fails when Jaha renders her brain-dead, so Abigail (now dechipped) transfuses Ontari’s blood into Clarke, who takes the 2.0 chip. She enters the City of Light, where Lexa appears to help her. They find the room with the kill switch, but then A.L.I.E. reveals that numerous nuclear power plants around the world are melting down. Humanity has just six months to live, and the City of Light could be their escape.

Clarke decides that even if it’s true, they can find a way to survive. She hits the kill switch and frees everyone under A.L.I.E.’s control. Everyone begins to wake back up. In the meantime, Octavia executes Pike for killing Lincoln.

The 100 Season 4 premieres Wednesday, Feb. 1, at 9 p.m. on The CW.