Given the task definition and input, reply with output. In this task, you're given a story (which contains five sentences only). Your task is to find all the characters which are available in the given story.

Sentence1: Tom was a guard at a prison. Sentence2: There was a small uprising. Sentence3: Tom tried to help the best he could. Sentence4: He tried to hold a prisoner down. Sentence5: The prisoner suffocated and died.
A prisoner, Tom