You can always make 12 tricks provided East has no more than two clubs. After winning the ♣A, you should cash the ace of trumps and lead a low trump to dummy's 10. Next you ruff a club back to hand and play two more rounds of trumps. When East did begin with one or two clubs, such as on this full deal:

When you play the last trump, throwing a club from table, East is in trouble. You know he began with seven diamonds a trump and, hopefully two clubs. If East reduces to three diamonds, you will play the A, K and another diamond. East wins the trick and has to return a spade, allowing you to take the last three tricks with the top spades and the ♦9. Whenever East keeps four diamonds, and so only two spades, you will counter by cashing the two high spades, reducing East to ♦QJ87. This allows you to make three of the last four tricks by leading the ♦2 to dummy's 10. When East takes the 10 with the jack or queen, he will be forced to lead a diamond, allowing your 9 diamonds to take a trick. Two more high diamonds will get your trick total to 12.

You should see that it was vital to ruff a club on the above layout, for otherwise East would defeat you by coming down to two spades, three diamonds and a club on the last trump. After winning his diamond, he would be able to play a club to his partner.

If you can bring in the daimonds without loss, you have 12 tricks.  So how do you play the diamonds?

On hands like these, you should try to work out the distribution.  To this end, you must duck at trick 1.  When West continues clubs, East shows out.  You know that West has 7 clubs.  Now play off the major suits. On this hand, West shows out on the third round of spades and the second round of hearts.  Hence his shape is 2137 so know you know how to play the diamond suit.

Equally, if West had followed each time a major suit was played, you would know of his diamond void and could pick up East's Q9xx.

There will be hands where West's shape is still unclear after 6 rounds of majors have been played, but by postponing the decision in the critical suit, you often gain all the clues you need.  Note that if you had played in 6♦, you would have to decide how to play the trump suit very early.  In the light of West's known long clubs, you would probably get the diamond suit wrong.

Ruff the diamond with the ♣A; over to  dummy using  the ♣6 and ruff a diamond with the ♣K. Continue with a club to dummy's 7, ruff a third  diamond with the ♣Q and play the AK10 of hearts ruffing with dummy's last trump and ruff a fourth diamond with the ♣J leaving your hand with the ♣2 and three small spades. 

Dummy has Kxx of spades and a high diamond and East has the ♣3 and the AQ10 of spades. Can you see it coming?  Toss  East in with the three of clubs, discarding a spade from dummy. East has to play the ace and a spade and dummy takes the last two tricks with the ♠K and a small diamond. 

One thing is certain.  If West has the ♣A, he cannot also hold ♠K, for he passed his partner's opening bid.  In that case you should play a spade to the Ace at trick 2., to give yourself an additional chance of dropping the King singleton. Looking at it from another angle, if the ♠K is onside, you dont need the finesse as then the ♣A will be right for you.  The distribution you have to guard against is as shown.

The first point to note is that South holds the ♠Q.  If he holds both red Aces then he would probably be too strong to respond 1NT and also he would then have at least 9 tricks.  You must therefore base your defense on the assumption that partner has a red Ace and thus an entry.  The next thing to realise is that it will take too long to establish a second spade winner.  Clubs looks like a promising source of tricks - if East wins trick 1 and returns a low club, then 3 further club tricks will be available once partner wins his Ace.  Now consider whether a club return gives declarer a ninth trick.  The answer is no because if declarer already has 8 winners at this point (say 2 spades and 6 diamonds), then he can always develop a ninth without you being able to take 5 defensive tricks (work out the possible holdings).  In practice, South is unlikely to have more than 7 winners at this point - 2 spades and 5 winners in one of the red suits. Hence a club might concede an eighth trick, but not a ninth.

You can see 3 tricks in the majors and the ♣K looks promising as declarer looks likely to finesse in clubs.  However, given the bidding, declarer may well eschew the club finesse.  A more promising defence is to overtake the heart and switch to a club.  When you win the ♠A, you can put partner in with a heart for a club ruff. 

South surely has 6 spades from the bidding and play.  He has taken a heart and will win 2 club tricks with the aid of the finesse.  Hence if declarer holds the ♦A or ♣K, the contract is solid and you must therefore assume that partner holds both of these cards if you are to have any chance.

When the diamond is played from the table, you must rise with the King in order to protect yourself from a possible ruffing finesse in the suit.  If the full hand is as shown and you play low on the diamond, partner wins and gives you your heart trick, but South later ruffs out your ♦K to establish a discard for his losing club.

Counting declarer's tricks is the key to finding the winning defense.

It look tempting to play low from dummy, but why would West switch to a diamond away from his King?  Instead of playing low at trick two, a strong alternative is to play the Ace and continue with the ♥J at trick three, throwing the ♦Q from hand.

This loser-on-loser play gives you a real chance of establishing a long card in diamonds without letting East gain the lead. West wins the ♥J with the ♥A and shifts to a spade. You win on the table, ruff a diamond high, Cross back to dummy with a trump to ruff another diamond high.  You still have the trump entries to dummy to ruff the diamonds good and get back to cash the long one, discarding a club.

If the diamonds had broken 5-1, you would have had to hope that the ♣A was onside. 

South can have no more than 4 hearts since he preferred to play in no-trumps.  He is also marked with 4 diamonds from partner's lead.  You can draw the infernce that South also holds 4 clubs, else why would partner not lead from a 5 card suit.  The picture is becoming clear.  South has 1444 shape and his singleton spade must be an honour to make up his quota of points.  It follows that you can defeat the contract by taking your ♥K, then laying down the ♠A, continuing with the ♠4 to partners honour card, and scoring 2 further spade tricks on the return.

The spade suit in isolation is a guess, but if you play low and North wins the Ace, he can return a spade and you will still need to find the ♥Q.  If however you rise with the ♠K and that wins, you can enter dummy with a trump, throw a spade on the ♦K, ruff a diamond and then exit in spades to force the defenders to open up the hearts for you.  Hence the ♠ K is a better play.

The ♠A might be onside, or the club suit might break.  You might think that there could also be a squeeze if West holds the ♠A and 4 clubs, but for the squeeze to operate, you would first need to lose a trick, else West will always have a spare discard, and you cannot give up a trick without the defense cahing a second winner - so that line's no good.

You do have one additional chance - the ♦QJ might fall in 3 rounds, thus setting up the ♦10.

The correct line is draw trumps, cash ♦AK, cross to dummy with a club and ruff a diamond.  If the ♦QJ have fallen, that's 12 tricks, if not then test the clubs before finally playing a spade towrds your King.

There will be no problem if the diamond finesse is right, so it looks natural to run the ♦9 at trick 4.  Suppose this loses to the King and East plays a heart.  You now have the choice of the heart finesse or playing the clubs to be 3-3.  Those with knowledge of the odds would know that the finesse is 50% against a 3-3 break at 36%, so the finesse it is.  Bad luck! West has the ♥K and cashes his 2 winning spades.

You should not have put yourself in this position.  The best line is to take AK clubs after winning the ♠A.  If both opponents follow it is safe the play a third round winning with the Queen.  Now you know whether or not the clubs are breaking and hence whether or not to take the heart finesse when East plays this suit.  Success is not guaranteed, but you have maximised your chances.  

You have of course been counting the hand.  South has shown up with 4 diamonds, 4 clubs and 2 hearts.  He therefore has 3 spades.  Declarer has won 9 tricks and will make his contract if he can win 2 spade tricks.  If your partner holds the Jack of Spades you will always beat the contract, so assume declarer has that card.  A low spade will gift declarer the tricks he needs.  The Ace achieves the same thing.  However, if you exit with the ♠Q at trick 11, declarer can win the King, but then will have to play towards his ♠J.  If partner holds good intermediate spades, that will be good enough for the defence to win 2 spade tricks.

You can see that the spade suit is blocked.  Therefore declarer will need a side entry in order to draw trumps.  You must attack that entry by leading the ♦K.  Declarer can win the Ace, cash 2 high trumps, but is then stuck on the table and has to conced you a second ruff.  If declarer had the singleton ♦A, then there would have been no defense.  This type of defensive communication severing play is termed a 'Merrimac Coup'. Well done if you found the switch.

The key play is to not cover the jack of hearts, making it impossible for the defenders to continue the suit, at least not immediately.  So play low from dummy and win with the ace in his hand. If the club finesse is onside, 4S will be cold.  If it is offside, the club suit will be good for a discard.  But first, you must draw trumps.  It takes three rounds to do this, East having the three.

Now lead the ♣ J.  In practice this runs to the King.

Is South going down now?

Not yet.  Since you still have the queen of hearts in dummy, the defence cannot cash 2 heart tricks at this point.

East returns a diamond after taking his king of clubs.  Now you must not finesse as if it loses, West is in to fire a heart through dummy.  Instead, rise with ♦A, cash the clbs to dispose of a heart loser, and then concede a trick to the ♦K.  This way you make the contract even with all 3 Kings wrong.

West has 3, probably 4 points in hearts, and from the club play it looks like he holds the ♣Q.  Since you need West to hold ♦K, East will probably have the queen of spades since West would otherwise be too strong for a weak 2 the way that most people play this bid.  You need to set up the diamonds.  After winning the club at trick three, finesse the queen of diamonds, which wins.  Now play the ace of diamonds and ruff a diamond.  These are three-three.  You have been lucky so far, but you are not home yet.  Consider the distribution.  West holds 6 hearts, 3 diamonds, and length in clubs by the looks of things - hence short spades. If East holds ♠Qxx you can't draw trumps finishing in dummy.  However, there is a solution.  Lead to the king of spades and then play diamonds.  East has the Qx of spades remaining and can ruff or not as he wishes. If he does ruff, South overruffs, draws trump, and goes to dummy with the nine of spades.  Ten very lucky tricks.

If you discard one of your low diamonds on the ♥A, you will go down, as you can see by examining the full deal:

To make the grand slam, you must discard the ♣10 on the ♥A. Now when you play on clubs and find that the suit splits 4-0 with all of them on your left, you can cash the top clubs, enter dummy with a trump, ruff the last club good, get back to dummy with another trump and - finally - discard your losing diamond. Well played!

As you can see, a club lead would have defeated the contract, but West would always lead a diamond after his partner doubled 2♦ . Would a double of 7♠  by East have canceled the earlier double (indicating high cards in diamonds) and asked for a different lead?

A situation eerily like this came up in the 2009 Bermuda Bowl in Sao Paulo, Brazil, where at both tables a bid was doubled for a lead and the final contract, a slam, was doubled again. At both tables, the doubler simply wanted to increase the penalty that was coming from the opening lead he thought he was going to get. At both tables, however, opening leader thought the second double canceled the first. Both doubled slams were made for an unusual flat board.

If partner's count signals are to be believed he has an odd number of cards in both hearts and diamonds. Given the bidding he should have five hearts and three diamonds. If this is true, declarer has 9 tricks ready to run outside of spades:  four diamonds, three hearts and two clubs.

When declarer has enough tricks in three suits to make his contract, shift to the fourth suit. Just do it!  Shift to a low spade hoping partner has the king and will return a spade and not a club. How will partner know which black suit to return? The rule is this:  if partner leads one suit and then shifts to a LOW card in another suit, he wants the second suit returned. If partner shifts to a HIGH card in the second suit, he wants the first suit returned.

After drawing trumps in three rounds, the trick is to get to dummy to discard any losers on the ♥K and ♥Q. If diamonds are 3-2, playing South's top three diamonds would ensure you could reach dummy with the ♦9. However, suppose the full deal is as shown:

The straightforward play in diamonds will see West take two tricks. As it turns out, when diamonds are 4-1, the best play is to cash the ♦A and then make a surprising play - the ♦J! On the above layout, when West wins the ♦Q, he is endplayed. A diamond will give you an entry to dummy, and so will a club or heart shift. No matter what West does, you will take 12 tricks. Of course, West may try to avoid the endplay by withholding his ♦Q. However, this will be to no avail. You will play the ♦K and another diamond to leave West on play with only hearts and clubs left, either of which will give you your 12th trick. If both defenders follow to the second round of diamonds you could then reach dummy with the 9 on the fourth round.

You might ask yourself, "What would happen if East turned up with four diamonds headed by the queen and 10?" Obviously, East would take the Q and return a club, and you would succeed only if East began with the ♣K.

If diamonds turned out to 5-0, and trumps were 2-2, you would lead the ♦J next if it was West who had the diamond length. In all other cases of a 5-0 break, you would continue with the ♣A and another club, playing with the odds that the hand with the void has the ♣ K. When that is the case, that defender must give you and entry to dummy with either a heart or a club.

An overtrick is only possible if East began with the ♦K. If diamonds are 3-2 with the king onside, using the Q and 10 spades as entries for finesses will produce 13 tricks. The problem comes when East began with four or five diamonds to the king. In that case, you will need three entries to dummy for finesses in diamonds. Suppose the full deal is as shown:

The best play at trick two is to lead the jack of spades and, once West follows, overtake it with the queen. When the cards lie as in the diagram, you can finesse the ♦Q, return to dummy with a spade to the 8 and finesse the ♦J. A spade to the 10 will allow a third diamond finesse and give you your precious overtrick.

If both defenders follow to the first spade, you will fall back on the ♠9 falling singleton or doubleton to give you the needed entry to dummy for the extra diamond finesse in case East turns up with four or five diamonds headed by the king. Otherwise, you will have to be content with only making 12 tricks.

Yes, West blew the defense. But how should West know that partner has a doubleton diamond and not a singleton? Notice that East has to return a diamond before playing two more rounds of spades lest South discard a diamond on the third spade. Well, the answer may scare you, but here it is. 

If East had a singleton diamond originally, he should win the first spade with the ACE purposely fooling his partner and then return the diamond. Now West won't worry about partner having the ♠K and will return a diamond which East will ruff. If on the other hand, East wins the first spade with the KING and returns a diamond, West can reason that East cannot have a singleton diamond or else he would have won the first trick with the ACE!