Great issue!
And surprise, surprise (or not so much), the Big Bad is the one who is lurking since the beginning – yeah, it's him, the goat boy. Soul Glutton and The Mistress are history, with the help of a wish made by Buffy and granted by... clone Anya.
And the origins of Buffy and Spike's future disagreement maybe has its source here:
The portal is open and it is getting harder and harder for Willow to keep it at bay. They all decide to enter the hell dimension and use Dawn's keyness; Giles thinks that in an entirely magic-based reality, she will have god-like powers, so she has to go through the portal and close it. Spike is totally against it, but he is overpowered by the others, who don't see any other alternative. They all go to the hell dimension, and their King threatens to kill them all, showing his huge army of demons. But Giles was right, and Dawn has power: she burns the King... and all demons run for their lives.
Now, the problem persists: the portal needs to be closed, and it has to be done from the hell dimension. Dawn says she wants to do it, and Spike doesn't want to hear none of that. He says to Dawn that she won't stay, and that she must listen to her elders – and calls Buffy for support. He is shocked when the Slayer says that Dawn is an adult and if she wants to do it, it's her call... Spike gets very mad, saying that they are crazy if they want to abandon Dawn in that hellhole! He decides that if she stays, he stays with her. But Giles and Willow point out that hell dimensions have a strange influence on vampires, mentioning what happened with Angel in Pylea and Quor'toth, so Spike can't stay. Xander then says he will stay (I think that may help Dawn to fall in love with him again, they being together fighting for their lives and looking for a way back to Earth...), because he isn't that necessary in the war against the Soul Glutton and the Mistress – which infuriates “ghost” Anya, abandoned again by Xander; she says she will get her revenge against him.
Giles, Buffy, Willow, Andrew, and Spike go back to Earth, and Dawn closes the portal. Buffy cries; she is with Willow. Andrew says to Spike that he should be with her, but Spike tells him that he isn't the right person right now, at home he will talk to her. When they are leaving, Buffy wishes that would be better if she could concentrate only in finding Dawn and Xander, and leave the Council deal with the Mistress and the Soul Glutton – and Anya grants the wish...
Anya is a perfect copy of the real one, and with her anger at Xander, she has become a Vengeance Demon, immortal and solid again. D'Hoffryn has big plans.
The Sould Glutton, before being squashed by D'Hoffrin, ate many souls in the Silicon Valley - isn't where Hank got a job?