She works in a large accounting firm, and her office is directly across from that of her high school crush. The two took a few classes together in school and talked from time to time, but one of them was always dating someone else when the other one was single, so nothing ever came of it. Now not only are they both single, but they both are up for the same small promotion. Lately, she has been having very vivid fantasies about him, fantasies where she is tied down, her body explored, and she is left in a vulnerable position and left to fear being discovered by another.
On the day where their boss is to announce which of them is getting the promotion, her nerves are a wreak. In an attempt to distract her, her crush offers her a bet on who will win. In her nervous state, she speaks faster than she can think, and proposes that she be bound at her desk after the place closes. She is horrified by the words that slipped out, but he takes them in stride and agrees. When news comes down that he actually got the promotion, she is almost more excited than disappointed.
I would like to see this progress into a series of more submissive situations, based on bets she knows she can't win. Perhaps the next time they bet, he gets to 'kidnap' her on an evening of his choosing. The time after that, she has to obey his every command for a day. Eventually it would lead into a caring dom/sub relationship.