I think Shawn and Lassie are at the police station and then Lassie ends up shoving Shawn up against the wall and... yeah. I remember the author saying the fic was inspired by this picture:
http://farm7.staticflickr.com/6054/7022275487_cc2f974b95_z.jpg t wasn't very long, just one chapter. It was very hot and I just can't seem to find it anywhere D: