By far my shortest summary because it's just not possible to cover the layers Ewing gifts us. But it's a fantastic issue that deserves to be discussed with art that deserves to be shown off. So here goes nothing!
We open with the preview pages as Storm is confronted by several anti-Phoenix beings all conjured up by the Shadow King. She starts to fight them as Max is confronted by Charles, form taken by the Shadow King. As they talk Max tells "Charles" to stop calling him Erik. "Charles" says that he met him as Erik and now he's going by Max which is his attempt to drop all his masks. But Charles says there is one more mask and asks Max what the name in his heart is. Max answers Magneto. Charles morphs into red costume evil Magneto. He shouts pro-mutant/anti-human rhetoric, Magneto's own words, forcing Magneto to face this side of himself.
The First Fallen notes how beautiful Storm is, how perfect she is. He tells her to never change and tries to freeze her like a statue but she breaks free. She says she will not be caged by him or anyone. Annihilation then appears and puts itself on Storm's face. It calls Storm out for being addicted to responsibility, flitting from one to another like a butterfly, like a magician spinning plates. Annihilation asks if the world can go on without Storm, if even if ever fought if she isn't around. The Shadow King comes to Storm as Charles and she tells him to stop insulting everyone he pretends to be and just show up as himself. He morphs into the Adversary and continues mocking her.
Magneto continues to face his red costume self and ultimately tells red that he's no longer just about protecting mutants, he has evolved to wanting to protect all that are hated and feared. This is super simplified but the conversation is much deeper.
Storm continues to smartly combat everything the Shadow King says to her until he finally takes his own form. He taunts her saying she's the only one that can save the world, that can save her people, the perfect Goddess who never fails. She and she alone. She realizes this is his last trap, trying to get her to fight him alone. She charges up, realizing what she needs to do, and puts out her right hand.
The Shadow King is gone and Storm starts falling after the intensity of the blast. Magneto catches her but she's weak, dying. Her narration tells her that she now knows that her Cosmos' mission is now fulfilled as is her own. She's slipping away as she tells Magneto to turn his key once more and return to the real world where he is needed. But Magneto refuses for it to end this way!
Storm awakens in the real world. The glowing hands belong to Taaia and it appears she, with Blue Marvel next to her, has revived Storm. We of course know it was Magneto. She sits up and tells Adam to look. A skeletal figure approaches from inside the gate. "The gate screams as matter is torn from the energy beyond, spinning flesh, bone and blood - new and yet somehow the original." Newly formed feet touch the floor as the figure steps out of the portal.