This month's coup is about misinformation. I'm not talking about deliberately telling your opponents facts which are incorrect, because we all have a lot more imagination than that. I'm not talking about psyching or misbidding either because these subjects have been dealt with plenty of times in the past. What I'm talking about is altogether rarer — misinforming yourself. Take this hand:

Both Vuln Dealer W	A 7 5 8 5 A Q 10 8 7 J 8 6			West North East South 11 1 Pass 2 Pass 2NT Pass 3 Pass 3NT AP Notes (1) 5 card majors, strong no-trump, short club style
Q 4 10 7 6 2 6 4 2 5 4 3 2		J 9 8 2 K Q J 4 K J 3 K 7
	K 10 6 3 A 9 3 9 5 A Q 10 9

The bidding may look a bit strange, but all will become clear. A heart is led and you duck two rounds before winning the A, pitching a spade. You run the 9, losing to the Jack and a heart comes back to West's 10 (you throw a club from table and a spade from hand). He now plays a low diamond in this position:

You've lost four tricks and so need the rest. Do you finesse the Q? Of the club and diamond finesses, the club finesse is clearly favourite, so that gives you four tricks, and the A K, A and A bring your total to eight. It's not easy to find a ninth trick that doesn't involve finessing the diamond now and why shouldn't you? West hasn't shown or implied a single high card yet and he's more than good enough to put you to this early guess by underleading his K here, so what's wrong with taking the obvious line?

What's wrong is that you've been doing some counting and know that East holds the K. You see, when 1 was alerted, you had a look at the convention card on the table and saw that the opposition were playing Precision. So you bid a Truscott-1 and happily went to game when partner made some forward going moves, thinking your middling cards were placed well over the strong hand. The trouble is, the convention card you looked at wasn't your opponents' convention card at all! It had just been left there on the table from the previous round.

Oblivious to this, you draw completely the wrong conclusion — that East must hold every high card outstanding — and rise with the A to run four rounds of clubs. When you play the last one, East is in trouble as he can't keep three spades and the K. When he pitches a spade you can play spades from the top and look rather shocked when West turns out to have held the Q. You mutter something about East being 'marked' with the diamond honours and head to the bar in the hope that it'll disguise your red face.

This Coup (which would be made even sweeter if you had accidentally checked your own card!) isn't restricted to just reading the wrong system. It applies whenever you mislead yourself into taking an anti-percentage line which works. How do you play the heart suit on this hand in 4:

Oppo cash two clubs and exit with a spade. The scoring is butler IMPs so you naturally take the best line for four heart tricks — you plan to cash the A, cross over to hand and lead up to the Q J 3 2. Today you're in luck because the K drops singleton behind the A and if you had finessed in hearts on the first round you would have had to lose another trump trick to West's 10 9 8 7. Of course, it turns out that you had misheard the announcement at the start of the evening: this week you're playing matchpoints!

And there are plenty of other situations:

The Convention Card Coup was discovered by Adam Dickinson at the 2005 London Easter Congress. He gained a swing for his team by drawing completely the wrong conclusion after reading a convention card from the wrong match. Tom Hanrahan played the second hand and managed to pick the trumps up for 1 loser.

"Money has replaced sex as a driving force, death has replaced sex as a taboo,
and sex has replaced bridge as a social event for mixed foursomes."
—Reginald Perrin

Ok, that quote bears no relation to this article whatsoever, but I like it. So there.