In an interesting twist, the people of Arkadia are forced to deal with the fact that despite all of the preparations and advanced tech, once things get bad, they will only be able to save 100 people. The number is ironic given that it was 100 kids in season one who were sent to earth to see if it was viable. Clearly, there are currently more than 100 people in Arkadia and this means that Clarke, the de facto leader, is going to have to choose who lives and who dies, a decision that she absolutely doesn't relish. The more Clarke tries to run from making a list, the more insistent that Raven is that this is what must be done. Raven makes it clear that Clarke is the expert at choosing who lives and who dies.
The Four Horsemen, is loaded with the idea that leaders often have to make unpalatable decisions and then must find a way to live with themselves for the choices that they make. Naturally, given the mayhem of the last season, the two who seem to suffer most alongside Clarke are Bellamy (who's still on the redemption train) and Jaha (who is inexplicably is still alive despite being pointless).
When Jaha attempts to leave on an expedition to find some under ground bunker he believes might provide shelter for thousands, for the five years necessary for earth to be survivable again, Clarke and Bellamy are quick to jump on the opportunity. Raven, who plays the realist this episode is against the trip, points out that by the three of them leaving, they are taking away not only a necessary vehicle but manpower at a time when every resource is critical. Clarke however will not give up hope and so promises Raven that if they don't find anything suitable, when she comes back she will make the list. Clarke should have asked herself when was the last time one of Jaha's schemes worked out.
In Polis, things aren't going very well. Roan informs Octavia and Indra that someone has stolen the flame. This is a massive deal because the flame is all that is keeping the red blooded Roan on the throne. Octavia is ready to go full on assassin and do what she has to, to bring the flame back. I cannot help but think back to the Octavia of season one, who while adventurous was nothing like the kick ass Lara Croft assassin that she is today. It seems that Roan is intrigued with Octavia and Indra is proud of her.
Having decided not to return to Arkadia, Emori and Murphy are having a hard time surviving. Murphy is quick to realise that his strength does not lie in hunting and that he is a much better thief. Murphy decides to return to Arkadia to steal the supplies that he and Emori need.
At Arkadia, Luna, the last nightblood arrives with the surviving members of her group who all have radiation poisoning. Luna begs at the gate to be allowed in because she believes only the medicine at Arkadia can help to save the last of her people. After a quick medical examination, Abby realises that the new arrivals all have radiation poisoning from ingesting poisoned fish. While it's good that the radiation is not yet air born, the pollution of the fish means that the radiation is advancing faster than they thought. Raven now believes that instead of having the six months she originally calculated, they actually only have two.
Abbie wants to treat the Grounders with anti radiation medication but they only have 14 doses which would mean using half of their supply to save Luna's people, even though the medication is most successful within 24 hours after exposure. Raven is quick to put a stop this, saying that if they are going to be stuck inside for five years because of radiation, they need every single dose that they have. Abby's instinct is to treat the sick, whereas; Raven's focus is on using the few resources they have wisely. Abby makes it clear that by denying Luna's people the medication that it won't be the radiation sickness which kills them but Raven's decision. What neither woman realises is that Murphy, who has returned to Arkadia to scavenge supplies, has heard all of this.
It's Murphy who steals the medicine and hands it over to a grateful Abby. Abby decides to treat the child with the hope that if it works, they can treat the adults. When someone comments that they are surprised that Murphy would steal medication, given that his father was floated for stealing medication to save his life, it's Abby who responds that she's not surprised in his actions. It seems that Murphy has undergone his own redemption, in Abby's eyes at least.
Back in Polis, Octavia has tracked down the thief and the two start to battle it out. It's Indra who calls a halt to the fighting because Octavia is battling her estranged daughter Gaia. It seems that Indra's daughter left Trikru to follow a religion based around the tech, much to Indra's disappointment. Gaia it seems has decided to devote her life, traveling the earth, looking for people who have Nightblood. The reunion between mother and daughter is decidedly not happy, with Gaia suggesting that Octavia is Indra's replacement daughter.
The unhappy reunion between Gaia and Indra is cut short when Ilian and a group of Grounders start pounding on the door. Gaia wants to use the tunnels to escape but Octavia has another plan. When the Grounders burst in, Ilian takes the flame from around Gaia's neck and promptly destroys it. What Ilian doesn't realise is that he's only destroyed Gaia's necklace and not the actual flame. When the Grounders leave, Gaia points out how smart Octavia's plan was but is no closer to handing over the flame. This puts Indra into the position of deciding whether her daughter has to die, or lying to Roan. At this point, Octavia's allegiance is clearly to Indra and so she indicates that she will do whatever it is that Indra wants. Octavia understands all to well covering for family.
Clarke, Jaha and Bellamy arrive at the compound. In a moment alone, Jaha tries to talk Bellamy into forgiving himself, arguing that Bellamy acted in what he believed was the best interest of his people. Is that what Bellamy was doing last season? Jaha suggests that as long as a leader has that in mind, they should be able to live with their decisions; however, thankfully, Bellamy points out the hypocrisy of this belief. Jaha has to take this tactic because there's no way he could live with the horrible things he's done over the last four seasons. Unfortunately for everyone, the bunker turns out to be yet another one of Jaha's wild schemes that turns out to be wrong. The bunker is not survivable and Clarke, Bellamy and Jaha find it filled with the skeletons of the long dead cult members.
Murphy returns to Emori and makes it clear that they are going to have to hang with his people for awhile because a storm is coming. Emori is worried about whether the people of Arkadia will take them in but Murphy explains that he's already made inroads with Abby. Damn it, and here I thought that Murphy had an attack of conscience when he stole the medicine for the child.
Octavia hands over Gaia's broken necklace to Roan, claiming that Illian and his people destroyed the flame. Roan takes the news remarkably well, though he knows that this means that he will have to fight to maintain his position. Perhaps, Roan's neutral response comes from knowing that he will have Octavia by his side in whatever is to come. It's clear that The 100 is setting these two up to have a passionate romance, or at the very least, some very dirty sex. And how do we know this?
Having returned from Jaha's failed mission, it's time for Clarke to sit down and write the list she promised Raven. Clarke pauses when she gets to number 99 and then fills in Bellamy's name. Clarke is even more disturbed when she gets to the final name. It's Bellamy who writes Clarke's name on the list, explaining that if he gets to survive, then so does she. Clarke then puts the list away until they have to use it.
Despite Abby's intervention, all of the Grounders die with the exception of Luna. Abby is quick to realise that there's only one thing separating Luna from everyone else who died, Luna is a nightblood, which apparently allowed her body to reject the radiation. Abby asks Luna's permission to run some tests. Could Luna's blood be the key to surviving the radiation? Somehow you just know that the damn tech is going to be necessary.