A na?ve girl helps a strange fugitive claiming to be from the future avoid arrest so that he can marry her future self.

"When she hides a fugitive claiming to be from the future, a little girl must help him turn her school's see-saw into a time machine and escape mobster justice."

We need some idea of what the girl has to do in order to save him. She can hide him in the basement, but then what?

Whether he promises to marry her future self or something else maybe redundant for the logline. It's their B-story.