Fake Buffy w/ Imortal, Spike knows she's not really Buffy. Real Buffy is in the air duct.

I read this ages ago and thought I'd saved it. Angel & Spike meet w/ the Imortal & "Buffy", but she's a fake. The real Buffy is hiding in the air duct to witness the meeting, Spike knows the fake Buffy is fake, and Spike smells the real Buffy's scent via the air duct. He stalkes her calling "here kitty, kitty". You'd think since I can remember all that I'd remember the name, but nope. Thanks for any help. It's one of my favs & I promise to save the link this time.

That's it! Thanks so much. You all are amazing w/ the finding of the fics!