Here’s a bidding guide for deciding whether to double an opponent’s contract. It’s called the Rule of Nine. It works as follows. Start with the number of cards you hold in opponent’s suit. Add any honors you hold in the suit. Finally, add the level of the contract. If the total is nine or higher, double to your heart’s content.

I was reminded about the rule when I made an inauspicious double in  a contract that looked beatable. I was sitting North and dealing, with no one vulnerable:

                                     S K 8 5 2
                                     H A 8 6 3
                                     D A 9 5 3
                                     C 3

WEST                                                     EAST
S A J 9 7                                                 S Q 6 3
H Q J 5                                                   H —
D K Q 4                                                  D J 8 7 6
C 10 5 4                                                  C K Q J 9 7 2

                                   S 10 4
                                   H K 10 9 7 4 2
                                   D 10 2
                                   C A 8 6

The bidding proceeded as follows:

North            East            South               West
1D                  Pass            1H                    Pass
2H                  Pass            Pass                 2S
Pass               Pass            3H                    Pass
Pass               3S               Pass                  Pass
DBL               All Pass

Opening lead: club 3

“How can I go wrong,” I thought. “They were passed hands and johnny-come-latelies to the auction. I have two aces and great spades, and partner’s surely worth a trick or two. Never have I felt more confident about doubling someone into game.”

What followed was a tale of foolishness and heartbreak. In truth, East-West were fools who never should have entered the auction. It’s foolhardy to overcall with a four-card suit. East got suckered into raising with three spades: fool! A seven-card trump suit is often a fool’s errand.

And yet, the rule applied. Partner gobbled up the club ace and returned another club for my ruff. Then I cashed my diamond ace, with a certain spade trick guaranteed. The heart ace was surely the setting trick.

Except that East was, well, heart-less. I haven’t the heart to describe the play from here, except for my single spade trick. Three spades doubled and making, for a heart-breaking -530 score that cost us a session-destroying 11.52 imps.

So let’s apply the Rule of Nine. I held four spades; the bid level was three, and I had one spade honor. The total of eight wasn’t enough.

The rule works especially well when your left-hand opponent makes a weak-two bid that your partner doubles for takeout. Let’s say LHO bids 2H, partner doubles, and RHO passes. You hold:

S 8 7 5
H K Q J 10
D 10 4
C 8 6 4 2

Now you’re cooking with gas: four hearts, four heart honors and a two-level auction. That’s 10. Convert partner’s takeout double into penalties.