In the above deal Declarer and Dummy together hold 9 cards in the ♦ suit, with only the Queen and three small cards missing. The question is : how do you play that suit :
 play for the Q♦ to drop on the second diamond trick
Win the first diamond trick with the K♦, then win the next trick with the A♦ or
 finesse South for the Queen
Win the first diamond trick with the K♦, then lead the 2♦ towards West's J♦
The following provides some guidance in this dillema.
"8 ever, 9 never."
When holding 8 cards (or less) in a suit with only the Queen missing finesse the Queen.
When you hold 9 cards in a suit with only the Queen missing play for the drop of the Queen.
But Easley Blackwood has refined this proposition.
Blackwood Theory of Distribution (when Opponents hold Q x x x)
Easley Blackwood invented a formula which can be applied when the Opponents hold four cards in a suit including the Queen. The formula is worth considering as it has been tested on a large number of published hands and found to be remarkably successful.
 When holding for example
 ♠ A 6 4 2 opposite 5 7 10 J K ♠
 Play for the drop of the Queen when the number of cards in your shortest suit in the combined hands is 5 or more, or 4 divided 22.
♦ 5 3 opposite 2 J ♦
 Finesse the Queen when the number of cards in your shortest suit in the combined hands is less than 4, or 4 divided 31 or 40.
♦ 3 opposite 2 5 J ♦
Blackwood based his Theory of Distribution on the, as yet untested, "Law of (hand) Symmetry".
Source : ACBL Encyclopedia of Bridge, Edition 2011

So how do you play the ♦ suit ?
