It really sounds like The Reluctant Hero by Dreamer
The Reluctant Hero
Summary: Spike helps Buffy out. NC-17
It's set post Helpless, but Buffy's attacked by a rogue watcher. Spike does rescue her and helps her get better. He does bring Giles and the Scoobs in later to help.
If this is the one that you want, the reason you can't find it is because it is on the old, old Vamp Kiss archive. Unfort., it's a WIP.
http://web.archive.org/web/20050108025430/vampires-kiss.net/fics/reluctanthero.html
If this isn't it, I'm really sorry for answering the question, Pari. It was one I looked for for ages until someone posted a link for the ancient Vamp Kiss archive. I'm pretty sure this is the original from before they got hacked again. Again, if it's not the right fic, I'm sorry and please delete my post.