Old sin

One pitch a day: in August of 2011, I dedicate twenty minutes each day to writing an "elevator pitch" for a story or a game.

A woman courts and marries a man who is the right hand of an organized crime overlord. She does so because a shadowy source told her her sister has been sold into sex slavery to the pervert boss and is detained in his fabulous mansion. The house is forbidden territory and neither police nor state will help the woman. The criminal organizes a week-long party for his 70th birthday, and invitations are given only to close associates and their spouses.
The woman has one week to rescue her sister before the party ends. But a rival of her husband performs a background check on her and tries to frame her as a policewoman. To prove her sincerity, she needs to kill somebody: one of the indentured servants of the criminal.
This servant was the shadowy source; his motivation was the love shared with the woman's captive sister.