Quick recap: Carol's powers have been on the fritz; it causes her pain to use them, which is why she's been running around not using them in the guise of Catherine Donovan. She's after an old enemy named Ghazi Rashid, with the help of a couple of uninteresting indistinguishable spy dudes from her past (Rick and Rossi). Ghazi, teamed up with Osborn, has ingested a formula called Ascension, which gave him superpowers.
Most of this issue is he and Carol trying to kill each other. Something about Ghazi has managed to piss her off enough to remember her old life - all the emotions and connections she lost when Rogue stole her powers - and she's got a serious mad-on for him as a result. Of course her powers, surprise surprise, go on the fritz again, and she starts overloading and going all Binary.
She puts Ghazi down, but isn't able to kill him; there are too many people around to stay and finish the job and she can tell she's about to go nova.
Annnnnd... that's it. No more Carol. The rest of the issue is concerned with Rossi collecting Ghazi for Osborn, Rick killing Rossi for double-crossing him and Carol, and Osborn telling Moonstone she's the only Ms Marvel. The final page is a splash of Moonstone flying off into the night in the old red Ms Marvel costume.
Please, please, please do not ask me to reconcile this with Carol's place as powers-functioning-totally-fine, very-not-dead-and-entirely-secure second-in-command-for-the-forseeable-future of Avengers Group #23,471. Probably she survived the explosion, landed just fine, and decided "to hell with this" and wandered over to Bucky's house to find an author who's actually marginally interested in her story.
Also, you know who really, really, really does not impress me right now? Brian Reed, that's who. Seriously, what the hell was that? Not only was that the most deeply pointless death I've seen in... I don't even know how long - it's not a war death, it's not to protect innocents, it doesn't take down or hinder the bad guys, it's not even a fridging, because who the hell does it motivate, Rick? Who gives a crap about Rick?* - but we don't even know what the hell actually happened, and somehow I don't anticipate Reed putting much page space into explaining it now that it's over and Carol's out of the book. Her powers freaked out! For no apparent reason! And killed her! Just because! Look, Moonstone is Ms Marvel now and Carol is boring and sucks so shut up, it doesn't matter, I don't care, I write what I want!
Great, fella. Fantastic character death. You're a veritable Shakespeare.
* Unless, of course, Rick's crusade against Osborn becomes a running B-plot under Moonstone's tenure as Ms Marvel, in which case I am even less impressed with Reed, which shouldn't even be possible, but there it is.