Image of the hand as known

You are South and after this bidding sequence partner leads the DA. What do you play?

West  North East  South
                    1H     P
1S      X       3H     P
3S      P       4S     All pass

 Such defensive tricks that belong to your side are in the minor suits. If you partner holds the CAK as well as the top diamonds he or she will know what to do. However if partner holds a major tenace in clubs, you need to be on lead for trick 3. You must make the play of dropping the DQ under partner's ace at trick 1 so that he or she knows it is safe to underlead their DK. Of course there is no guarantee that West does not hold the CA. If this is so no defence will stop declarer from making eleven tricks.

From JW Tait Bridge Challenge (Board 2). This book published in 1974 was one of the gems available for free in the Peninsula Bridge Club library cull - declarer and defence play problems do not age as much as books on bidding.