Imagine a world where, through selective sex abortions, the rampant spread of HIV, and warfare, the population of women has fallen dangerously low. There are only a few women to every thousand men; those who are still alive are assigned four or five or even six husbands to make up for the shortage in a strictly regimented, heavily authoritarian society.
Now imagine a woman who refuses to be part of this system: who lives on the edges of this world, in an underground Sanctuary made up of the few women like her who remain unregistered and hence officially do not exist.
But they emerge from their Sanctuary at night. To provide a service that only the very rich and the very fortunate can afford: to sleep, through the night, with a man in his bed, providing him with intimacy and attention that almost seems like a myth in this day and age.
(your hook starts here)
Sabine is just such a woman. Intelligent, rebellious, beautiful, and independent; her most attentive client, Joseph, wants to possess her in every way possible, and will visit havoc on her body and her life in order to own her. Julien, the sensitive, emotionally damaged doctor who falls in love with her, struggles with accepting his feelings for a woman who represents everything he is never supposed to have. Can Sabine navigate through dangerous waters and the desires of men, and find her way to freedom and safety?
Interesting premise but when something is very rare, people generally take VERY good care of it, thus wrecking havoc on a woman isn't logical. Also, HIV infects men and women both so it's not something that would diminish the number of women disproportionately to men.
You need to be focused and specific about the story. You've got the set up, and world building but not much else.