OK, I read this fic sometime in the last year on spanderfiles. The part that's stuck in my head is that Spike and Giles figured out that they were related. I vaguely remember a bit with them in the training room at the Magic Box, joking and being friendly with each other and Giles calling Spike 'Uncle'. Unfortunately that's all I remember, the rest of the story is blur.
This has been driving me nuts for the last week! I would really love to reread this story, so any help would be much appreciated.