Is this a good idea for a story?

All story ideas are good and this one is no exception but its how you write them that matters. This idea has a lot of potential and would undoubtedly make a good read. I do have doubts about the clown though and the reasons are that anyone dressed as a clown would be too conspicuous and also it smacks of a Stephen King Novel I read once. I would get rid of the clown and replace him with something else even if it's something like a Tesco employee or a sailor. Whatever you decide just sit down and write it and good luck with your story.