After the battle of L.A., Spike wakes up hundreds of years into the future, with no memory of what happened after that fateful day. He lives on to become a Time Agent, becoming partners with a man named Jack Harkness, and becoming a time traveler in hopes of finding Buffy and discovering what happened over the years he's missing. (Basically, Spike is John Hart).
As Earth's children are threatened, and the world approaches crisis, Buffy finally discovers what's making her ill.
Seo's trying to make a point. And she's making it using Torchwood.