I'll be skipping some of the details Spurrier provides that aren't necessary to the overall story.
Right at the beginning Mother Righteous tell us that she has been ready for her move for centuries, that her "sacred weapon" has been loaded and armed for ages. She didn't really need all of the items she had the Nightkin collect and she was using their sacrifices to weaken the impervious force-field protecting the Moira clones. She insults them several times as she tells us that she's endured "a whole millennium waiting for the rest of this rotten timeline to get its $@%& together. A millennium hiding my true intentions."
Dr. Nemesis, who has now grown into a giant face and head that covers her ship, tells her that he has discerned something of importance. Thanks to the Nightkin carrying his spores with them into the Worldfarm as they sacrificed their lives, they have known the location of Sinister's lab/Moira clones and have been watching it. Nemesis tells her that diamond Sinister has finally arrived and shows him on the monitor fighting in the battle that happened in last week's SatB issue. He asks her if she's missed her chance, if diamond Sinister will reach the laboratory before she can deploy her unscientific payload. But she has time since the force-field is still intact and she tells Nemesis to use every spore he has in space to scan every quanta starting at the Worldfarm and expanding outward. She's confident, via her faith, that he'll find something they need.
Mother reminds the reader that Destiny had stolen the Moiras to give Mystique the longest life possible. She's been banking on a single article of faith...
We get a data page titled "Destiny Knew", a simplified map of the universe. We see Sol and the Worldfarm. There's a yellow line that starts at Sol and zig-zags across the universe that is now about to reach the Worldfarm. This yellow line is labeled "The Lonely Bullet." Then there's a purple line labeled "The Eater of Sin" as well as the "Vengeance Swarm" also about to reach the Worldfarm.
The religious trumpets sound and all the remaining Nightkin line up to sacrifice themselves, greatly weakening the force-field even further. There is one left, Auntie Fortune, and Mother has her teleport them to the Worldfarm. Auntie asks Mother if it worked but Mother says the force-field is still holding. Then Banshee/Vox appears with Galactus, having been taken over by all the Spirits of Vengeance that fled earth at the start of Sins, chasing him. Vox tells Mother that he tried to secure an alliance with the other spirits but that they still abhor him and have been chasing him for 56 years. Mother is super rude to him and says she knows all this. This was basically a distraction to keep him away and to keep the Spirits occupied.
Then he appears. Juggernaut! "A thousand years ago the Sinisters shot an unstoppable object right through the brain of a Titan. They didn't stop to wonder where it'd go next - but Destiny did. Destiny knew." WOW! He had spent a millennium moving through gravity wells, slingshotting, building speed. Destiny orchestrated a "cosmic trick shot - an impossible conjunction"...
Destiny was crazy for this! I'm impressed. Most of the force-field has been destroyed but a bit more remains. Mother coldly and nonchalantly orders Auntie to sacrifice herself and finish it off. Auntie hesitates but being so bound by centuries of faith she does it and the rest of the force-field is destroyed. Vox is horrified by all the death surrounding them, the skulls of the Nightkin floating around.
It is now that Mother reveals the Reliquary Perilous, a glowing orb, as they approach the lab. The self-sacrifice and generations of faith of the Nightkin powered it. But its purpose is not to destroy the Moira clones and "cleanse the Sinister strain" from the galaxy as she told her followers. Now that the force-field is gone the chaos of the war outside will eventually destroy the clones. The purpose of the Reliquary Perilous is to work as a holy virus that will infect its way backwards when the timeline is reset and rewrite it all. "It was never about endin' the story, Vox. It's about changing the start." Vox starts to understand, saying that's why she asked all those questions to all those people, for centuries. She intends on sending those secrets back in time to herself. She responds, "Finally gettin' it, ain't you? This ain't a cleansing purge - it's a cheat code. So that in the next go-'round? Hearts are trumps."
Data page describe how the weapon, the "Ace of Hearts", works. It clings to any relativistic or chronological alterations to the present universe, infecting its way backward along the dying timeline toward the source-moment. It carries with it whatever power, information, or magical actions encoded in it, executing these functions at the moment of arrival. A message in a bottle. "Or, depending on who made it and what they put in the bottle, a bomb."
(I'll speed through the last parts here.) Mother uses the Heart to pull the Spirit from Vox, using it as fuel to make the trip back in time, leaving him only as Banshee. The mind that will steer the payload is the golden baby that was introduced last issue. It has a pure, radiant soul, saturated in faith of its fanatics. It will kill the baby in an agonizing death and as Mother starts to fire up the Heart, Wagnerine appears! "Get the $%&@ away from my baby." She slashes Mother who then uses the Heart to magically hold Wagnerine in place and in pain. Mother plans to unwrite her story and she can do so because the thousand times Wagnerine thanked her she gave up control of her soul to Mother. As she's talking, Banshee crawls over and stabs Mother in the foot. She is now holding him the same way she's holding Wagnerine but while she's focused on him and what he's saying, she's stab in the back and through the chest by Wagnerine's tail claw. "Nobody ever remembers the tail."
She stabs Mother some more while she's dead on the ground, the Heart on the ground next o her, and Sean tells her to stop, basically telling her not to waste her time on Mother any longer. Wagnerine holds her baby and Sean, weak and old, tells her "nothing matters so much as bein' in charge o' your own story..." She teleports away with her child. Sean, sitting against a wall, is alone with Mother's corpse and the Heart. It's quiet. Then someone approaches, picking up the Heart.
"Being in charge of your own story. Hm."
Sean: "M... Moi...?"
He is shot in the forehead.
"Well said, Sean."