The girls were looking for fun, riding in the car. Sometimes they got themselves excited. Apparently they wanted a new sensation, so they offered a threesome to a strange young, handsome guy. After some persuasion and conversation, he agreed and went straight to work. The girls hooked up with him, gave him blowjobs, rolling on top, while two were fucking, the third fondled the couple.
I've been waiting for the cover scene for so long, and it's not there. Just a staged shot.