"By Jove, Holmes, I don't see how you knew. That lead of yours violated the textbook rules."
"You cannot put the same shoe on every foot, Watson," Sherlock Holmes said mildly. "Perhaps I may be forgiven since my lead defeated an otherwise unbreakable contract."
Holmes and Dr. Watson were reviewing their match against Professor Moriarty. The Professor had played at 3NT after North-South bid all four suits. Holmes, West, pondered his opening lead. (Before you read on, decide what lead you would choose.)
Finally, the great detective tabled ... the six of spades.
Moriarty cackled as he won with the ten, but when he led the queen of hearts next, Watson won and returned his last spade. Holmes forced out Moriarty's ace, and when he got in with the ace of hearts, he ran the spades for down one.
"I should have gone after the diamonds instead," Moriarty observed sourly, "but as the cards lie, my contract was hopeless after that aberrant opening lead."
"Of course, Watson, my lead was hardly an aberration," Holmes remarked. "Our best chance lay with my spades, but since Moriarty had bid the suit, I had to hope you held the ten, or perhaps, as was the actual case, any doubleton plus a side entry.
"If I lead a 'textbook' king of spades," Holmes went on, "Moriarty prevails by refusing the first trick. Rules are all very well in their place, but this was an exceptional case."