In Avi's The Man Who Was Poe, Mr. Dupin, who is actually Edgar Allan Poe, represents the lesson of how to cope with one's fears.
Throughout the story, Avi portrays Poe as a very fearful man. He is especially afraid of death due to his grief over the death of his wife, whom he called Sis, just as Edmund calls his sister Sis. Poe's fear of death is portrayed in his frequent feeling of being haunted by ghosts or demons. In addition to a fear of death, Poe is afraid of enclosed spaces and heights.
Poe conquers these fears by immersing his own identity in the identify of a detective character he created for a series of his mystery short stories, a character named Auguste Dupin. It is as Auguste Dupin that Poe solves the mystery of what happened to Edmund's Sis and Aunt Pru. As Mr. Dupin, Poe sees there may be a connection between the gold robbery of Providence Bank and Sis's kidnapping and visits the bank to examine the vault, posing as Mr. Grey, an inspector for an insurance company. Inside the vault, Poe has an episode of claustrophobia, imagining the vault as a tomb, and nearly faints. Despite his spell of fear, he is able to notice a piece of string he later determines is a piece of strong rope. The piece of rope helps him draw the conclusion that Sis was stolen to be lowered into the vault through the air vent via a rope so she could help her kidnappers steal the gold.
So long as Poe remains immersed in his character Dupin, he is able to actively solve the mystery. Yet, the moment he returns to being Poe, the writer, he tells Edmund, "I'm a writer, not an adventurer" and refuses to help Edmund actively rescue Sis (181). Poe's refusal to help stems from the fact that, as Poe, he has returned to being incapable of coping with his fears.