For this one, I would be travelling through the country at night, or via backroads. My vehicle would break down or lose a tyre, and I would see an expansive home or mansion. The occupant would welcome me in and give me a laced drink, and introduce me to my new life as their fetish maid, slavegirl, pet.
A possible variation of that is a family who lost their 18yo daughter, or wife, and make me into their replacement, which works in a rural environment, being semi isolated.
If either of these ideas appeals to anyone let me know.