When not to make a penalty double

When the opponents have reached a contract that you do not think they will make, it might seem sensible to double, thereby scoring more points. But it is not quite so simple - what if they then run to an alternative contract?

North bid aggressively to Small Slam via the Blackwood 4 NT convention which asked partner how many aces they possessed (5 ♥ showed two). But when East doubled 6 ♥, North reassessed. It was clear East’s ♥s were strong enough to defeat 6 ♥ so North tried the effect of making ♦s trumps - even though it meant bidding a Grand Slam. East doubled again - perhaps less confidently - and West led ♥ 7.
South won ♥ K, cashed ♣ A, trumped ♣ 4 with ♦ 2, led ♦ 4 to ♦ 9 (noting East discard - ♠ 5), trumped ♣ 5 with ♦ 8, and overtook ♦ J with ♦ Q to draw West’s remaining trumps (North discarding ♥ 65 to leave ♠ AJ109 and ♥ A). He then led ♠ Q to ♠ A and ran ♠ J - a “ruffing finesse”. East covered with ♠ K (South would have discarded ♥ 2 if East had played low), so declarer trumped, crossed to ♥ A and enjoyed ♠ 109. He had actually made his doubled Grand Slam! East was left to rue his double of 6 ♥ - he should have passed and quietly defeated the 6 ♥ contract with his two trump tricks.

ANDREW’S TIP: Do not double a contract unless you will be happy if they run to an alternative contract.