When I was a single girl I lived for a year in the San Jose area. I didn't have car at that time, but the bus system was very good so I went everywhere on the bus.
Usually the buses I took weren't very crowded. I kept a mild flirtation with a young man(very gorgeous) who took the same bus to work. My best friend's husband warned me he was a player so I didn't get in too deep! I'm sure I would have been one of a harem of women...
Sometimes I would head somewhere on a crowded bus and I tried to sit by myself or by a woman, since there were some strange people on the buses. One day I sat down by a man who was neatly dressed in a suit. I didn't look too closely at him, but there were few choices since it was so crowded. I was just glad to sit by someone who seemed to be on his way home from work, ordinary.
"Do you believe in parallel worlds?" He asked. And I realized my seat-mate wasn't quite sane.
I have often thought that would be a good opening scene, a call to adventure.