Two students make a bet: whoever gets a higher mark in their next essay gets whatever they want for a day. When Nimue wins she decides to make Sebastian her slave for 24 hours. She's going to enjoy this...
Sebastian is sure he's going to ace their next essay - so sure that he goes out to play football instead of studying. When Nimue objects he challenges her to a bet: whoever gets a higher mark gets whatever they want for the day.
When Nimue wins the bet, she decides to milk it for all it's worth. After all, Sebastian needs teaching not to be so cocky in future. She makes Sebastian her slave for the day - and lays down the rules he must follow as house slave, or else be subject to punishment. Nimue dresses her slave up in sexy underwear, makes him to the dishes wearing only tight boxer briefs and a maid's apron, then puts him in a butler's outfit with tight trousers and smart waistcoat, and has him bring her tea and shine her shoes. Sebastian thinks the whole thing is stupid, but he lost the bet fair and square, and he goes along with it.
Eventually, Nimue decides to make use of the spanking implements she's scavenged from around the house, even though he hasn't disobeyed her, he starts to object. But according to the rules of their bet, there's nothing he can do about it.