Luna's wounds seem bad (enough to cause that worry on Bellamy's and Clarke's faces) but at the same time she's able to sit up. Is that a good sign for her potential recovery?
Murphy is back in Arkadia! We last saw Murphy and Emori on the season premiere, abandoning the rest of Skaikru when they sensed things going downhill with Ice Nation in Polis.
Nyko, one of Trikru, seems to be OK and not stricken by the radiation. It appears that he's brought Luna and her afflicted Grounders to Arkadia for help from the Sky People.
Luna isn't the only one of her group of oil rig-dwelling Grounders suffering from radiation poisoning. A little girl is also suffering from it, and by the looks of it, doing poorly.
Whatever they're discussing, it seems really serious and dire, based on the expressions on our heroes' faces. Perhaps it has something to do with Luna and her people looking so rough.
Since the hydrogenerator plan was a bust, perhaps they're working on coming up with a new alternative to keep their people alive through the nuclear meltdown.