Stowaway is not based on a true story. It's a work of imagination crafted by the filmmakers to captivate the audience with a unique narrative and plot.
I'm not sure specifically as there could be many stowaway short stories. Generally, it might be about a person who secretly boards a vehicle like a ship or a plane without permission, and then various adventures or challenges they face during the journey.
In a stowaway short story, the main character is most likely the stowaway themselves. They could be a desperate immigrant trying to reach a new country, so they stow away on a ship. There could also be a sympathetic crew member who discovers the stowaway but decides to help them instead of reporting them right away. These two could be the main characters, with their relationship and the moral dilemmas they face being central to the story.
The main theme could be survival. The stowaway might face numerous challenges during their unplanned journey, such as lack of resources, hiding from the crew, and dealing with the confined space. All these elements can be related to the basic instinct of survival.
There could also be other passengers if it's a passenger - carrying vehicle. These passengers might be completely unaware of the stowaway, or they might get involved in the discovery or hiding of the stowaway later in the story.