As the episode begins we see Toad locked in a cell by the MRD, claiming that it will only be a matter of time before he's out of there. The guards are apparently so used to his running his mouth that they ignore him. They're also quickly distracted by the fact that there is another mutant literally knocking at their door, but unlike most others, he's begging to be locked up. In fact he's not happy with being put in a cell near other mutants, he wants total isolation.
This is Nitro, a mutant whose abilities make him literally explode. In the comics, Nitro is not a mutant and is also a supervillain, but I think taking his powers and putting him in this context does make for a great story device.
Toad witnesses Nitro's first explosion at the compound and sees the MRD bring him to an isolation tank, so when Quicksilver shows up in front of his cell he's eager to spread the news. This is actually a really funny scene, as Toad is all excited that Quicksilver is coming to break him out, but no, he's not, he's here to tell him that the Brotherhood has decided he's useless and they're just going to leave him here. And he also snaps a picture, because Blob wanted to see the look on Toad's face when Quicksilver told him. This is exactly the kind of thing I could see someone with Quicksilver's powers doing. When Toad tells him about Nitro, he let's Toad out after all, and they grab Nitro to use him as a tool in one of their schemes.
The MRD has a database of mutant names and locations, and the Brotherhood wants to blow it up. They tried once before but couldn't get through the defenses, but now with Nitro they can literally blast through them. Rogue isn't on board with this idea at all, because she recognizes immediately that this is not what Nitro wants and she understands how it feels to have powers you can't control. The two of them have a nice conversation to this effect, and while the Brotherhood does use him to blow up the database, Rogue demands that they get him some help on controlling his powers.
Their solution, it turns out, is to call in the help of Psylocke. She's in her Asian body with her original British accent, something I'm not sure is ever acknowledged in the comics but I like it. I also like that she's not truly evil here, it's just that Quicksilver once helped her bust out of the MRD and so she's paying him back for that.
Meanwhile, the Professor has sent Logan another message from the future, letting him know what's going on and what they have to do - something he says is contrary to what he always taught them. They have to return Nitro to the MRD where he can be contained yet again. You know, you would think maybe Beast could come up with some kind of containment suit for Nitro and that way the man wouldn't have to be imprisoned, but of course this guy is just supposed to be here for this one episode so let's put him back in jail.
The Brotherhood are trying to bring Nitro to Genosha, because Quicksilver thinks for sure that destroying the MRD's records and handing over a living weapon will make Daddy love him again. I'm teasing but it's actually a really nice angle, and a good way to explain their relationship without piling on too much exposition. On their way the X-men pull up in the blackbird and a decent fight occurs where the X-men take Nitro away from the Brotherhood. Probably my favorite part is where Kitty phases through the Brotherhood's plane to grab him, and casually calls "Hi Rogue!" on her way through.
Psylocke's attempts to help Nitro control his powers were unsuccessful, and he does end up exploding again, but since they are in the middle of the sea on an ice float Iceman created, no one is hurt. Logan explains to Quicksilver than if they hadn't come to intercept them, Nitro would have killed half the mutants on Genosha. Didn't really think that one through too well, Pietro. The X-men return Nitro to the MRD and everything is back to relative normal for now.