First of all, you have to tell /play *where* to play the file. You didn't include $nick or $chan, so it won't work. Also, not that you should have a space after the last color (:) in the event or you may have problems. You also don't need /'s in a script. One last thing to keep in mind... you have it triggering on !show *. That means that someone has to type !show then a space and something following it. If that's what you meant to have it do, then that's ok. Otherwise, remove the * and/or the space.
If you want something to happen after the file is played to the user, then look at /help on playend .