“The Four Horsemen” is episode three of season four of The 100.
In the previous episode, “Heavy Lies the Crown”, Octavia had decided to personally deal with the Trishanakru ambassador, so that the still-injured Roan wouldn’t have to fight him. By stabbing said ambassador in the ear and removing the blood so that it looked like he had died of natural causes. Currently it does, but will this last? Clarke, in order to get more help, had revealed the truth – well, most of it – to the rest of Arkadia. The bit she omitted about the oncoming disaster was that they didn’t have enough resources to support all the Arkadians. Especially as Bellamy and the others had used the hydro generator they went to get from Farm Station as a bomb to help free the prisoners from the Ark being held there, rather than returning with it as planned.
This episode opens in Arkadia with preparations being made to secure it against the oncoming radiation wave. At the moment it will support a maximum of a hundred people, and even then it poor conditions. Then some Grounders arrive at the front gate. They are in poor condition and need medicine. They looks sick, and they are, but it’s not a disease – they’re suffering from radiation sickness. The fish in the sea are dying. Time is far shorter than they thought. Six months to prepare now looks a little bit optimistic. The sickness would appear to be from the fish. One of the Grounders is Luna, the last known Nightblood, and she is with the last of her people. Raven adjusts the timeframe down – to two months before the black rain arrives. She wants Clarke to come up with a list of those who are going to be allowed inside the Ark.
Jaha, being an engineer, knows that the Ark will not support everyone. He has an option that will help the others. He says that there is a bunker within a day’s drive of Arkadia. He had data on a bunker, privately built by a doomsday cult, that is nearby. The downside is that he isn’t sure the bunker exists, and they originally didn’t need it, which is why it wasn’t considered when the original hundred landed on Earth. Now, they do need it, and Jaha thinks he’s found it. It needs checking out though, and they are short on time to check. Still, being able to save a lot more than one hundred people is worth a risk, so Clarke, Bellamy and Jaha head out in a rover to look for it. If the bunker is there, is it intact? And was it ever used? If the last, might it still be occupied?
In Polis, Roan approaches Octavia. He wants her to handle something for him – he knows that she killed the ambassador. The Flame has been stolen from Roan’s quarters; Roan believes by a Flamekeeper. If this becomes general knowledge, things will rapidly fall apart, as it will be taken as a sign that Roan should not rule by the other tribes, leading to open war between his forces and those of the other tribes. Octavia agrees to help. Roan admires her skill at killing; Indra is less happy about the killer she has created. The matter is more complicated, and Ilian and his followers are destroying technology so that they cannot be enslaved again.
Murphy and Emori are on the move, both being survivors, and Murphy’s relationship with Ontari is brought up. They lack supplies, so Murphy heads to Arkadia to steal supplies. That might not go down too well at the moment. Murphy does overhear Raven and Abby talking about just how bad the situation is. So he knows the he and Emori will need somewhere safe to ride out the radiation. Murphy steals some medicine that Abby wanted and gives it to her; perhaps to ingratiate himself.