He fucked this young girl naked with the train moving
Surely if you have traveled or travel often by train on more than one occasion you have had this fantasy. Sharing space with a young and pretty girl is undoubtedly a good way to improve the trip, but when this young woman is also so extremely slutty that she is willing to get naked and have sex on the same train, things become like paradise.
This is how this mature man had a sexual adventure with the young girl, who ended up completely naked on the train (just like him) and they ended up fucking without any fear of being discovered or caught, which undoubtedly could have been very likely.