I'm not sure specifically as there could be many stories named 'the passenger short story'. It might be about a journey of a passenger, perhaps facing various challenges during travel, or having some unique encounters on the way.
Given that it's a 'passenger short story', the main character is most likely the passenger. But there could also be supporting characters. For example, if the story is set on a ship, there could be a captain or a crew member who interacts with the passenger in a significant way. Or if it's a story about a plane journey, there could be a flight attendant who has an important role in the story. Without more details about the specific 'the passenger short story', it's hard to be certain about all the main characters.
Not having read it, I can only guess. There might be a protagonist among the regular passengers who has to deal with the extra passenger. There could also be a character who is initially hostile to the extra passenger, and another who is more sympathetic. Maybe there is an authority figure like a conductor or a ship captain if it's a story set in a vehicle or on a ship.
Well, without having read 'the extra passenger short story', it could be that the extra passenger is a mysterious figure. Maybe they bring a new perspective to the main characters. They could be a source of conflict, like if they have a different goal than the other passengers. Or perhaps they are a symbol of something, for example, a symbol of an unexpected change or a new opportunity that the characters have to face.
I'm not sure specifically which 'passenger to be free story' you are referring to. There could be many stories with such a title or theme. It might be about a passenger who is on a journey towards freedom, perhaps escaping from some form of oppression or confinement.