It's a common fault of new players to be offended when their partner leads a suit in which they have a single honor. For example, the contract is 3NT and the partner leads a low card in a suit in which the third hand has K432. The dummy has only a couple of low cards. Now third hand is annoyed that her king is getting picked off. It's not uncommon to see the player in third seat play a low card, holding on to that king for dear life. That's just wrong.
When your partner makes her opening lead, you should be pleased that you have something to contribute to the cause of the defense. Suppose all you had was the 5432 instead of the K432? Won't that king help your partner's hand if you play it? You are East in the following diagram. Consider the effect of playing low versus playing your king after your partner leads the suit.
Your partner leads the ♠ 6 against 3NT. If you get stingy with that king, the declarer will win a trick he isn't entitled to. If you play the king, not only will it win but you will still be on lead to play another spade through the declarer's Q10 to your partner's AJ. You will take four spade tricks.
In general, it's best to play the highest card in the suit your partner leads — remembering that when holding a sequence of cards your proper play is the lowest of “equals.”
When Not to Play High
Before you start becoming annoyed about all the exceptions to all these rules, remember that experience and common sense will help you work out most of them. These seemingly complicated ideas will become second nature to you.
Your partner leads the ♦ 6 against 3NT. Dummy comes down and it's your turn to play:
We've learned about third-hand high, so your correct play is the king, right? Not quite. Let's think about what your partner has led from and what the declarer might hold. Using the Rule of Eleven, which you learned earlier in this book, you know that there are five cards higher than the ♦ 6 outside your partner's hand. Dummy has one — the queen — and you have three: the king, 10, and 8. That's four. Therefore the declarer has one card higher than the 6. What is that card? Does it matter? …Yep, it does.
Say your partner has led from four spades to the jack. That means the declarer has the ace — but it's the only card higher than the 6 in her hand. If you play the 10 — the proper card in this case — it will drive out the ace. You will be poised later over the queen in the dummy to assure that her highness takes no trick. You don't want to play the 8 because if your partner has led from the AJ, the declarer might make a trick with the 9. That would be embarrassing!
If you simply recite, “Second hand low, third hand high,” and make that your mantra, you will play the king, and the declarer will be able to take two tricks in the suit.
Suppose your partner's opening lead was from the AJ. If you put in the 10, it will hold. Then you can play the king and another spade to your partner's ace and you will take four tricks in the suit.
If your partner's lead was from AJ and you play the king, your king will win, but when you play the suit back, your partner will have to play his ace in front of the dummy's queen, and the queen will turn into a trick.