I'm pretty sure that is Anything to Save Her by dark dreamluver. It was on Just Rewards but the links aren't working for the chapters through Wayback unfortunately, but the summary is this...
Buffy breaks up with Riley and he doesn't take it so well. He drugs her and kidnaps her taking her to a remote location in the mountains. He tells Giles and the others that he is taking her away for the week for a romantic getaway so they won't be suspicious. He didn't take Spike into consideration. Spike must convince the others that Riley means Buffy harm and when they don't believe him, he goes to the only other person that might help him: His Grand-Sire-Angel.I don't know if it is available anywhere else still.
OK - I found it
here.
