Two guys were being led into the police station bickering, almost in fisticuffs. Barney was like, "Hey hey, what's going on here?" Turns out they had a game of chess going BY MAIL. A dispute ensued between the players when one of them sent a winning play which was supposedly never received by the other. It was something like a knight to Queen 3 (I don't play chess so forgive me if this is way off), in this case a checkmate. His "check," said the arresting officer, "is in the mail."