I am in the middle of Stephen King's excellent new book 11:22:63, which I can thoroughly recommend, by the way.
It is his first venture into a time travel story and he delivers with his usual flair and excellence. I have to be (almost) physically prised away from it and, at well over 700 pages, it will be a few days before I reach the story's destination.
For anyone unfamiliar with the premise of the story: Jake Epping is given the chance to go back in time and prevent the assassination of President Kennedy. He decides to do so, knowing that every encounter he makes, every event he changes along the way, will have repercussions and will change history for all time.
Not the first time this type of 'What if...' scenario has been tackled of course. To cite just one example: many books have been written - and conjectures made - about how the world would look today if Germany had won World War II (or WorldWar I for that matter) but, as you might expect from a master storyteller, Stephen King provides his own unique slant.
So - a little challenge for you. If you had the chance to step back in time and change one key event in history, what would it be? How would the world be different today? Would there be any downsides to your proposed change?