One of "those" parties.
The young couple found the address without any problem, and parked their car amongst a dozen others along the curving driveway.
New to the area, and not knowing anyone, they had looked at advertisements in the personal column of the local newspaper.
In amongst them they found exactly what they were looking for.
"Fun loving couple seeks other fun loving couples to meet for intimate and discrete time. Must have own car."
There had been a vetting process where they had to send photos of each other, and answer a number of questions about age, gender, and sexual preferences.
The couple had never done this sort of thing before, but were happy when they were immediately accepted, and given the time and date where they should attend.
On arrival they were greeted at the door by a middle aged couple. The woman was well preserved and looked very attractive in her rather revealing clothes.
Having been introduced to the assembled group, made up of men and women of all ages, the young couple was shown a glass bowl half filled with car keys, and asked to drop theirs in amongst them, and then mingle and chat to other guests so everyone could get to know each other.
After a quarter of an hour or so, the man who had met them at the door called for silence, then said the new couple should get to go first.
Pointing to the glass bowl, then to the newcomer, he said, "Pick a set of keys. Just make sure they are not your own, then pair off and go somewhere private in the car you have chosen."
The older man swirled the keys around with his hand, then held the bowl in front of the younger man, who pulled out a set of keys attached to a BMW key-fob.
Looking around, the young man saw an older but still attractive woman waving to him.
Several hours later, having exhausted themselves in enthusiastic lovemaking in, on, and outside the car along a secluded lane, the young man said, "I hope the chap who took my car has enjoyed himself as much as I have.""
Slowly sliding her underwear back on, his companion said, "I don't know, but I'm really glad we did this."
"So am I", said the young man. "I never thought I would ever get the chance to drive a BMW, let alone make love in one when I married you."