The couple who aren't supposed to be together sneak into the supply room and start to make out, unaware that the new intern is in the dark corner by the boxes of copier paper....
The couple is a lesbian couple (that's why they're hiding their affair), and the intern is a pervy dude. He insists that they both pleasure him in order to buy his silence....
Or the couple is a hetero couple, but married to other people. And the intern is a bi pervert. He insists they both pleasure him in order to buy his silence....
Or.... well, I can think of about five more combinations, but they are all pretty much the same in the end.