Here's what we know so far -- the Avengers launched an unprovoked attack on the X-Men, kicking off the whole AvX event. This caused Scott Summers to start absorbing the Phoenix Force from the others and become the Phoenix himself. He then went and killed Charles Xavier. Marvel has been saying that the Red Skull is going to become more of a super villain in the Marvel Universe with this series. And in tomorrow's release, we see what that means.
A few people who have seen the book (it was available on Comixology for a short time before it was supposed to be) have dropped hints. And now, a retailer upset with Marvel has sent in the big spoiler at the end of the book. I want to emphasize that I have no proof this is legit, but it does pass the smell test (it jibes with the veiled hints others have been giving), but still take it with a grain of salt.
According to the retailer, the story ends with the Red Skull in possession of Charles Xavier's brain and implanting it in someone's body in a very graphically portrayed sequence.
No wonder I'm not working for Marvel. I know I certainly wouldn't have come up with that.