In The Man Who Was Poe by Avi, why does Rachett leave his coat at the clothing store?
The Man Who Was Poe, by Avi, is a mystery story in which one of the characters (not surprisingly, given the name of the story) is Poe himself, though he calls himself Mr. Dupin. In this story, people are not always who they seem to be, and that is true of the man who is called Mr. Rachett.
Dupin is working on a case for a boy named Edmund (as well as gathering information for the next story he will write), and he has figured out a few things Edmund has not. Dupin sends Edmund to a local tailor's shop; when he walks in, a rather heavyset man is trying on a coat and talking with the tailor about the recent local bank robbery. When he turns around and sees Edmund, the man is visibly shaken and quickly turns away. The tailor hustles Edmund out of the shop to make his customer more comfortable; when he looks in the window one last time, Edmund again sees the man looking nervously around the shop.
Many things happen between this event and Dupin's later arrival at the tailor's shop, but since this is a mystery I will try not to give away any secrets. The tailor tries to sell Dupin a coat which he said a man ordered but did not pay for; the man was in the shop that morning but left quickly after a rather ragged young boy came into the shop and made him nervous. Obviously that boy was Edmund, and Rachett left his coat behind because he was startled at seeing Edmund and feared Edmund would somehow recognize him.
Poe says "lies have their own truth," and we later discover this is true about Rachett--and his coat.