A popular format for short stories is the twist in the tale ending.
It must come as a complete surprise to the reader but has to be set up properly. A few clues or signposts should be sprinkled throughout the short story so the reader doesn’t feel cheated.
Sometimes the best way to start these stories is from the end, decide on the twist then work backwards, considering all the clues you can give the reader without revealing the truth.
Also, remember to keep the plot simple and not include too many red herrings or lots of suspicious characters.
This page has suggestions for the type of twist you might employ, so click below and see if you can come up with a short story that will leave your reader satisfied and impressed with your deviousness!