Synopsis
Captain America, accompanied by Beast, Black Widow (not on the cast list), Falcon, Giant-Man, Hawkeye, Iron Fist, Iron Man, Luke Cage, Mockingbird, Ms Marvel, Red Hulk, Scarlet Witch, She-Hulk, Spider-Man, Spider-Woman, Storm, Thor, Valkyrie and Wolverine, recruits the help of Hulk.
Rogue comes to the Avengers' stealthed aircraft in the Wisconsin plains, saying that Madison Jeffries tracked Iron Man's energy signature, and asking for a truce. Professor X shows himself as aligned with the Avengers already. And loads more X-Men (Cannonball, Gambit, Havok, Iceman, Karma, Polaris, Psylocke, Warlock, Warpath, X-Man and a blonde who is probably Boom Boom (not on the cast list)) come out from the vegetation behind Rogue. Hope Summers appears with the Avengers too. They all know that Cyclops and Emma Frost, the last 2 holders of the Phoenix Force, must be stopped.
On Utopia Island Emma accuses Scott Summers of wanting to take the Phoenix Force all for himself. Scott denies it, suggesting Emma is projecting her own intentions on him. But Emma reveals that her urge is more to destroy the imperfect world and rebuild it from scratch.
Their conflict is interrupted when Cyclops detects Prof X nearby. Scott confronts his mentor who tries one last time to talk him down. But when Cyclops tries to attack Xavier he finds he can't. And Charles reveals that they are fighting within Scott's mind.
Cyclops breaks free and back to reality. Where he finds Emma Frost facing a selection of the combined Avengers and X-Men, with Dr Strange, Magneto and Vision (missing from the cast list) thrown in for good measure. In fact Dr Strange seems to be holding Cyclops magically prisoner.
Cap tells everyone to keep attacking, to keep the Phoenix 2 distracted while Prof X regains mental control of Scott. Summers tries to manifest the Phoenix, but Xavier battens him down. Emma tries to come to Scott's aid, but Storm hits her with lightning (saying it's something she's wanted to do for a *long* time).
Cyclops fires his eye-beam at Xavier, but Cap reflects it back with his shield, and it hits its originator. Scarlet Witch sends energy coursing all over Scott's body. And Emma retaliates by frying Wanda. But Hulk smashes her into the ground.
Cyclops returns in Phoenix-mode after Prof X, but is confronted by Magneto, who says he invited Xavier to Utopia to oppose Scott. Summers engulfs Magneto in Phoenix-fire. Scarlet Witch attacks to save her father. When Cyclops is down, Thor leaps to the attack with a rallying cry to others. But Scott easily beats him back with a wall of flame.
Then Hawkeye gets him in the back of the neck with an arrow, which Cyclops casually snaps off. He asks Xavier why he's helping the Avengers try to kill the X-Men. But Iceman chooses this point to attack, saying that it's just Scott (and Emma) who are the target. And the rest of the X-Men are on the Avengers' side.
At last Charles has Scott back on the mental battlefield, intending to put him in a coma. But it is Prof X who loses the battle!
Battered and surrounded by foes, Scott Summers attacks Emma Frost, and takes her portion of the Phoenix Force from her, leaving her for dead. Charles Xavier tries to stop him again, but Cyclops, possessing the whole Phoenix Force, renders him possibly dead or mindless too.
Scott is horrified by what he has done, but blames the Avengers. If only they'd left him alone, none of this would have happened. Sensing the last chance, Wolverine gets Hulk to throw him in a fastball special. But Cyclops burns him in midair without even looking.
The assembled heroes, including Emma Frost, watch in dismay as the Phoenix-fire consumes Cyclops, and he arises as the Dark Phoenix.