Brian Jacques 
Lies of Henry Mawdsley (Storycuts) [EPUB ebook] 

Henry Mawdsley is a terrific liar. However, the more people get to know him, the less they believe in his lies — and it won’t be long until nobody in his town believes a word he says! So when a chance encounter with the devil offers him the opportunity to have everyone believe his lies unconditionally for a week for the measly price of his soul, Henry jumps at the chance. But as the week draws to a close, and the date of Henry’s descent into hell gets closer, he begins to fear for his life . . . Part of the Storycuts series, this short story was previously published in the collection Seven Strange and Ghostly Tales.