Season 4 of The 100 hasn’t started on a very hopeful note. A.L.I.E.’s warning in the Season 3 finale that the world’s nuclear reactors are melting down and that there are only months left to live has proven to be true. To make matters worse — and add to our nerves and the characters’ problems -– it turns out that even A.L.I.E.’s calculations that there are six months to live are wrong. With the arrival of Luna and the remaining survivors of Floukru, all of whom are suffering from acute radiation sickness, comes the hard truth that their time left to save the human race has dwindled down to two months. But “The Four Horsemen” offered a possible salvation in the form of Nightblood.

The episode opens with Nyko arriving to the gates of Arkadia with a small group of very sick Grounders. Their journey there saw the deaths of 40 of their people, and even more were lost on the oil rig where Luna’s people reside. Their diagnosis is acute radiation sickness, marking the arrival of the predicted nuclear apocalypse and presenting a threat that they are unable to fight. As the episode progresses, each of the Grounders brought to Arkadia for help die slow and torturous deaths — all except for Luna, who is not only alive at the end of the episode but nearly completely healed. Her body rejects the radiation, and there is only one factor that she didn’t share with the others: she is a Nightblood.

The story of the Nightbloods is one that we know very little about. Aside from the fact that we know their blood is black and it is ultimately what allows them to accept the Flame should they win their conclave, the only other information we’ve received about them is the information given to us in “Thirteen.” Their story begins in space on the Polaris Station, and it is directly linked to A.L.I.E. and the survival of the human race.

“I think that the end of this episode, the dots are there to be connected to how the world is what it is right now in terms of who were the Nightbloods and how being a Nightblood [was] something that became hereditary. Who were those first people that came out to meet Becca when she steps out of the pod,” showrunner Jason Rothenberg said in an interview with Nerdist shortly after “Thirteen” aired. “On the wall of the temple in Polis, Murphy points to the people around this woman figure on the wall, and Titus said it was Becca Pramheda, the First Commander. Titus may not have called her that, Becca Pramheda, in that episode, but that’s who she will become known. She’s got the Commander’s jacket on, right? She’s taken with her the blood treatment that she’d been giving herself which turned her own blood black as the first Nightblood. She’s taken all of that with her, and as she’s surrounded by these people that we know to be the first Nightbloods, I think the dots are there to be connected. Certainly some of our incredibly thorough fans will not miss out on the opportunities to connect it all together.”

Nightblood, while still surrounded in mystery, is genetically modified blood that allowed Becca to come to a radiation-soaked Earth. Nightblood is what allowed the survivors of the bombs to survive the radiation that followed. Nightblood is what ensured the survival of the human race, and likewise what can possibly assure their survival in this second impending apocalypse. Luna survived the radiation, which means that anyone who is a Nightblood can do the same. But there’s a problem — Luna is the only Nigthblood, and the only way to become a Nightblood, if it’s not passed down hereditarily, is by the same blood treatments that Becca had given herself on the Polaris Station.

While we can assume that Abby and Jackson and anyone else who knows about this news will work tirelessly to discover what exactly Nightblood is and how to reproduce it, currently there is only one way to continue the blood treatments, and it presents a moral conflict similar to the one seen in Season 2 in Mount Weather. Do you sacrifice the few to save the many? At this point in time, Luna is the only known Nightblood, which means they either have to figure out how to reproduce Nightblood (perhaps her accepting the Flame and ascending as Commander will allow her to “speak” with Becca) or take the Nightblood straight from her. Do they want to be Cage and sacrifice their morality, or do they want to keep their morality intact and risk the lives of hundreds?

If a simple transfer of blood, similar to the treatments that Becca had given herself, is all that it takes to become a Nightblood, this raises an entirely new question: is Clarke already a Nightblood without knowing it? In the Season 3 finale, in order to accept the Flame and enter the City of Light, Clarke had Ontari’s Nightblood pumped through her body much in the same way blood treatments were done in Mount Weather. A Nightblood’s blood pumping through your veins for an extended period of time is a lot more than just a few simple small injections of Nightblood.

Either way, “The Four Horsemen” presented a possible way to ensure the survival of the human race, and one that includes not having to narrow down who survives to only 100. What will happen going forward remains a mystery, but this is The 100, and, even if we think we know what will happen next, chances are that they will through us for a loop.