It's about Sirius Black's relationship with Bellatrix Lestrange as he remembers it on a very important day. It's not graphic or anything so I decided that R was way too high a rating but I would say it's a high PG-13
It's an AU, this portion takes place at the very end of third year. Harry reminisces about someone important to him, sorta. The title is that because everytime Harry Dances I picture it playing.