Both sides vulnerable.  
North deals.
                              North
                              S: A K 10 4         
                              H: A Q J 8 2   
                              D: K Q         
                              C: A K     
            West                             East
            S: 9 7 2                         S: Q 8 6 5 3    
            H: K 9 3                         H: 7 6 5      
            D: 10 6 3                        D: 9 4               
            C: 6 5 4 3                       C: Q 10 2      
                              South                         
                              S: J    
                              H: 10 4       
                              D: A J 8 7 5 2
                              C: J 9 8 7  
          The Bidding:  
                  North    East    South    West                  
                   2C      Pass     2D      Pass
                   2H      Pass     3D      Pass
                   3S      Pass     3NT     Pass
                   4NT  (All Pass)
          Opening lead: 6C
     The final contract would not have been so bad had South
played correctly.  He won the opening lead and played the king of
diamonds.  When both defenders followed, he called for the queen
of diamonds and played low.  Both defenders followed again and
declarer had four good diamonds in his hand with no entry.  
     His first attempt to get to hand was to play the jack of
hearts.  West refused to take this trick and declarer called for
a small heart to the ten.  West won this trick and played another
club.  This was won in the dummy and a small spade was called
for.  East played the queen of spades and cashed the queen of
clubs for the last defensive trick.
     Making four no trump was an absolute bottom.  South should
overtake the queen of diamonds.  If diamonds do not split he can
fall back on the heart finesse, When that works he will still
make twelve tricks.  As the cards lie, diamonds split and he can
make all thirteen tricks.
     A better question is how to get to six diamonds.  I think
the error is the three spade bid by North.  After South bids
three diamonds, if North bids three no trump, South could bid
four clubs as Gerber and then five clubs, resting in six diamonds
for a great board.