Captain Marvel #12 is on final order cutoff this Monday, October 28th and Killerspec got a hold of an advanced copy, which is well ahead of it's December release date. It's definitely a shocker issue with a returning character that could possibly see some uptick demand on his first appearance, becoming a prominent antagonist and villain in the Avengers world, but we'll have to see how the arc plays out as this is the first issue of such story.
Below is the cover art for the regular cover, by Mark Brooks. Keep scrolling for early spoilers. If you don't like spoilers, then you may want to leave now.
So the issue starts off in battle from the get go and it's pretty much a battle through the entire issue. It's Captain Marvel vs Thor. Thor is unaware it is Captain Marvel as her face is covered up until about midway through the fight.
After many equal blows between them, spanning across states, countries and continents, Thor gets in a nice knock down blow where he tells Carol to give up and yield, she's no match for a God. What could be a very important line (which is possibly future telling of why she's doing this) is she responds with, "I can't", as if she has no choice. The fight takes them into outer space by this time and Captain Marvel throws an energy projection from her hands to blast Thor's trusty hammer Mjolnir off into space.
Thor reminds Carol that separating him from Mjolnir is a waste of time and holds his hand out, telling Carol that his hammer always comes back. This time it doesn't. Thor is surprised, asking Carol what has she done? Her response is simply, "Evened the odds".
Carol then strikes down Thor, all the way back to Earth. She's seen carrying him away to bring forth the following spoiler panes...
Here we find out that Vox is the one behind asking Captain Marvel to kill Avengers.
Vox's first appearance was in Death of the Inhumans #1 if this turns out to be the same Vox who is now Vox Supreme.