By day, I'm a domestic violence prosecutor. By night, I read romance to restore my faith in love, relationships, and humanity in general.
Catrina is a Domme. She's a long-time, respected member of her local BDSM club, the Den, she has plenty of play partners, and though she may occasionally have some twinges about the lack of emotional connection in life, by and large she seems pretty content with her lot.
Damien is a Dom, in fact the Dom, the owner of the Den. In the early scenes narrated from his POV, he mentions that the Den doesn't have a lot of Dommes but that he has totes respect for those there are, and he'd never, ever, ever try to undermine their authority by treating them like subs ... but he has horny pants for Cat and he's The Dom, so... yeah.
He asks her to sub for him. She tells him to fuck off. He asks her pretty, pretty please (and says it'll make her a better domme when the experiment is over). She says fuck off (but starts to think, well, maybe....). He gets all masterful and sexy and shit, and her resolve weakens (because she's a girl, right, and all girls secretly want to be dominated, of course), and so she agrees to be his sub for two weeks.
Then, though she starts the two week experiment totally planning to go back to being the dominant when it's over, they predictably start to fall in lurve, and she starts to wake up to the glory of submission while Damien doesn't compromise at all (sometimes he thinks about how dickish he's being and how he really ought to be more decent, but then, somehow, he's all, nah), until by the end of the book she's not interested in dominating men anymore and he's the Best. Dom. Ever.
Fuck that shit.