Do you finesse or play high?

We are looking at situations in which third hand should or should not follow the "third-hand high" mantra. Which is right here? South is in four hearts. West leads a fourth-highest diamond two. After dummy plays low, should East put in his nine or rise with the king?

North knew that his hand was a tad strong for a four-heart "weak freak" raise, but he knew that it was unlikely his side had a slam, and he was worried that the opponents might be able to do well in spades.

East should work out who has what in diamonds. He knows that South has the ace, because West would not have led a diamond away from the ace. And South presumably has three diamonds. West probably has the queen, and might have the 10 as well. (If West had started with 10-high diamonds, he likely would have led from a stronger suit.)

However, the key point is that if East plays his king, declarer must get two diamond tricks: his ace and, later, dummy's jack. But if East puts in his nine, perhaps he can hold South to one diamond winner.

Yes, West will be momentarily misled about the diamond position, but East will clarify when in with his heart king, cashing the diamond king and playing another round of the suit.

You can see that in this layout, playing the diamond nine is critical. It allows the defenders to take one heart, two diamonds and one club.

The usual rule is: When dummy has one honor, third hand holds a higher honor, and dummy plays low, third hand saves his honor when he can insert a nine or higher.