Ok, I know all of that was extremely vague, but my memory is vague.
I remember that the fic is set in the future. Buffy is in the middle of a mission and needs backup. Who comes? Spike. He has some amazing high tech gun and rides his motorcycle. Everyone else shows up in a van. Buffy is shocked to see him and is worried that he doesn't have feelings for her anymore, but later she finds out that he doesn't have any feelings due to some weird circumstance... Obviously, in the end, all works out.
I know that is not a whole lot to go on, but can anyone help?