Make a "Discovery" play.
Bridge Column for January 28, 2001, By HARVEY BERNSTEIN
Both sides vulnerable.  South deals.
                              NORTH
                              S: A 10 9 7         
                              H: 8 4 2       
                              D: 4 3         
                              C: A Q J 10
            WEST                             EAST
            S: 4 2                           S: K 6          
            H: A Q 10 9                      H: J 7 5      
            D: 10 8 7 6 5                    D: K J 9 2           
            C: 7 3                           C: 9 6 5 4     
                              SOUTH                         
                              S: Q J 8 5 3 
                              H: K 6 3      
                              D: A Q       
                              C: K 8 2    
          The Bidding://
                  SOUTH    WEST    NORTH    EAST                  
                   1S      Pass     3S      Pass
                   4S      Pass     Pass    Pass
     West led the six of diamonds.  East is faced with a very
common situation:  What card should he play to trick one?
     It is the expert style to lead third or fourth best from any
holding against a suit contract (assuming that there is no better
lead).  Many players would prefer to lead this way only when the
suit is headed by one of the top three honors.  There is,
however, one universal rule:  Don't underlead a side suit ace
against a suit contract!
     So East knows that South has the ace of diamonds.  It is the
queen that is in question.  At trick one East should play the
jack of diamonds.  This is known as a "Discovery" play.  He needs
to find out who has the queen of diamonds so that he will know
how to continue when he regains the lead with the king of spades.
     If South wins the first trick with the ace, East knows that
he can cash the king of diamonds when he regains the lead.  
     In actuality, South wins the queen and takes the spade
finesse.  East knows that the only way to beat this contract is
to switch to hearts.  Since he has no way of regaining the lead
later in the hand, he must lead the jack of hearts.  If South
doesn't cover, West will play low and East will still be on lead
to continue the heart suit through the king.  If East errs and
leads a small heart, South will play low and West will have to
win the nine.  The contract is then unbeatable.
     It is amazing how much information a good defender can glean
from the bidding and the play to the first couple of tricks. 
That is why it is important, as declarer, to try to stay a step
ahead.  The primary consideration is to think before you play
your cards.  It is such a simple rule to follow, and yet it is so
often forgotten.
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