Were you tempted to switch to a heart?  If you do, declarer wins the Ace and plays a trump to his King, exposing the trump position.  He uses his 2 entries to hand (a heart ruff and the ♦K) to finesse against your trumps and makes his contract.  The winning defence is to play a diamond at trick 3.  This removes one of South's entries prematurely and he can no longer make the contract.

If West holds ♠QJTxx and ♦A, then your contract is in danger if you duck at trick 1.  On the second round of spades East will unblock the ♠K and this sets up the spade suit for the defence.  You cannot prevent West getting in with his ♦A and cashing enough tricks to defeat you.  If you plan to play the ♠A at trick 1, East cannot afford to unblock the King on the first trick as dummy's 9 then becomes a second stop. When East plays small, it is therefore best to play the Ace of spades at trick 1. However, you should be aware that this might not always work against very good defenders.  If West held KQJTx of spades and no entry, it would be a good play to lead the Queen at trick 1 to induce declarer to play the Ace immediately as above.  Then when South eventually plays diamonds, partner could win and would have a spade to return to allow West to cash his winners. Bridge can be a tough game.

West's bidding and opening lead tells you quite a lot.  Most players would lead a top diamond if holding AK, so wou can reasonably assign one of these cards to East.  Since there are only 18 points missing and West has at least 15 of them, it looks as if East holds the ♦K and no other values.  Hence you win the opening lead, ruff a heart to hand and run the ♠9. You can then repeat the finesse to pick up West's trumps.  With a decent lie in the heart and club suit, you will probably make 11 tricks, but 10 tricks are assured with 5 spades, 2 clubs, 2 hearts and a diamond ruff.

The bidding and play to trick 1 marks declarer with a 6115 or 6214 shape.  You expect to make your 2 aces but where is the setting trick to come from?  

Your best hope is that partner hold ♣Kx.  In that case, you can ensure a trick for partner's ♣K by leading the ♠Q at trick 2.  Declarer has no quick entry to dummy for the club finesse.  If he leads a heart, you can hop up with the Ace and lead another spade for partner to overruff dummy.

Clearly you need to determine whether partner holds the ♥K or ♣K.  If you win the first spade you will have to guess.  However, partner has played the ♠2, suggesting an odd number, so it is safe to duck this trick.  On the next spade partner will have the opportunity for a suit preference signal - playing the 7 if he has the ♥K and the 3 if he holds the ♣K.  You defend on that basis.

It looks like declarer started with ♠AT doubleton, and hence a spade return at this point concedes a ruff and discard.  Does that mean you should play a diamond?  The problem illustrates the need to count which is at the heart of good defence.  South is known to hold 6 hearts and 2 clubs, so has 5 cards in the pointed suits.  If he has a doubleton spade, he will hold 3 diamonds and one discard is not enough - you will still make a diamond trick provided that you exit with a spade at this point.  On this actual hand, declarer has made a clever falsecard in the spade suit to try and fool you into switching to diamonds.  Counting declarers hand is the key to success.

Your combined trumps will take care of the minors so you must avoid 2 heart losers.  Fortunately, the bidding indicates that West started with at most 2 hearts, so the contract is assured.  After the ♠A, play a trump to dummy, ruff a club, ♦A and another club ruff.  Then ♦K, diamond ruff and another club ruff eliminates the minors from the N/S hands.  Now a heart to the Ace and a second heart to the Queen is a sure winning line as either the ♥K is with East or else West will win with a doubleton ♥K and then be forced to concede a ruff and discard, so your remaining heart loser disappears.

Declarer won the opening lead with the ♠K over North's ten and led a club to dummy, followed by the ♥Q.  This was ducked all around and a second heart was won by North, who exited with a low spade.  Declarer was quick to seize on this misdefence when he finessed the ♠9.  East was then able to cash 4 more black suit winners so that 5 diamonds in total could be discarded from the table.  A diamond to dummy's Ace was followed by a trump.  South won the Ace but had only clubs left.  The forced club lead allowed declarer to ruff in hand - discarding dummy's last diamond and so trick 13 was made by ruffing a diamond on the table.  Well played!

The heart suit in dummy is threatening but by holding up your Ace, you can run declarer out of hearts.  All that remains is to ensure that declarer cannot get to dummy via the spade suit.  At trick 1 you should play the ♠9 rather than the standard book play of 'third hand high'.  Once dummy is eclipsed in this way, declarer will have to muster all of his tricks from his own hand and will fail.

Were you tempted to switch to a diamond after taking the ♠A?  

You know that declarer started with 2 clubs and 5 hearts.  Hence South holds 6 cards in spades and diamonds.  It doesn't matter how these 6 cards are distributed.  If you rise with the ♠ A and exit with a spade, then you must eventually win a diamond trick to beat the contract. 

So East has opened a weak 2♠ with just a 5 card suit (quite common these days).  Still you have a spade trick, 2 hearts, 3 diamonds and 2 clubs so that is 8 - one short of target.  You might get an extra trick if the clubs break 3-3, but if East were to win a club trick, he would defeat you with a club and 4 spades.  On hands that are short of their contract by one trick, a squeeze is often the answer. If West holds length in both hearts and clubs (not unlikely on the bidding) then he will come under pressure late in the play.  For the squeeze to operate, you need to first of all lose 4 tricks, else West will have spare discards available.  Hence you should duck the ♠9 at trick three.  If East continues with a spade, you should duck again, bringing your loser count to 4.  If instead, East switches to another suit, you can win and duck another round of spades to the same effect.  Once you have lost 4 spade tricks, the play of 3 rounds of diamonds will force West to give you the ninth trick.  You do however need to watch the discards so that you will know which suit West has abandoned.  Easiest is just to look out for the club suit.  If you have seen the QJT appear by the time you play out the top clubs, then you will know your ♣9 is a winner.  If the club isn't high, then West must have given up his hearts, so your ♥9 will win trick 13. 

You are in fact endplayed at this point as any lead costs a trick, assuming declarer reads the position correctly.  However, try the effect of exiting with the ♠9.  Declarer will surely rise with dummy's queen, and when this holds, he will repeat the finesse, playing East for ♠Kxx.  Now when you win you have a safe heart exit and can sit back and wait to make your ♦K for the setting trick. Leading a low card from honour doubleton looks suicidal on paper.  It is surprising how often it is the means of escape from an embarrassing situation.

It looks like there are no further tricks to be had outside of the trump suit.  If partner holds the Ace of trumps, there is no problem.  Could partner have any other trump holding that would produce a trick? Yes- partner might hold ♠KT.  Play the thirteenth club and partner can ruff with the ten if declarer discards in dummy.  If dummy ruffs with a spade honour, then partner can discard to the same effect.  It is a defensive rarity that the correct play is to lead into a triple void.

East's bidding surely pinpoints the missing key cards  Draw trumps in 2 rounds (East is void), the play off the spade queen, discarding a heart from dummy.  Now Ace and another heart will force whoever wins this trick (probably East) to lead a club or give you a ruff and discard.  If West is able to win the heart trick and play a club, then ducking in dummy will similarly endplay East.

You win the Ace of trumps and if you are to have a chance to beat the contract you must put partner in to give you a club ruff.  How you do this depends upon which club partner played at trick 1.  If partner played a low club, you cah the ♠A (denying the King) and lead a diamond to East's presumed Ace to get your ruff.  If partner held the King of spades then he should have played a high club at trick 1.  If this was the case, then you must underlead your ♠A to get partner in.  In the latter case, a club ruff will be your third trick and you will have to hope that either the ♠A stands up (unlikely) or that partner holds a slow diamond trick.

You have a spade loser and 1 or 2 clubs to lose depending on the club break.  On the bidding, West is quite likely to be short in Clubs.  You start by winning the ♠A and drawing trumps (West holding a singleton).  Now you should cash the diamonds and top clubs.  No problem if clubs are 3-2.  If West has a singleton Club, you just exit with a spade and West will be forced to give you a ruff and discard, so you will just lose 1 spade and 1 club.

If you lose the lead before taking 8 more tricks you will certainly be defeated.  You currently have 3 spades, a heart, a diamond and 2 clubs as top tricks so need 2 more.  Obviously if the diamond finesse works you will be home and dry, but you can give yourself an extra chance by playing clubs first.  Cash the Ace and King of clubs.  If the Queen falls, you can take 2 more club tricks using the spade suit as an entry.  Now you have 9 tricks.  At this point you can lead the ♦Q.  If West has the King, he will probably cover giving you the rest of the tricks, but if he plays small, you must rise with the Ace and take your 9 tricks.

Did you try to cash ♦A at trick 2?  If so, score -1430.

South could have bid 4NT, but he did not do that.  Players who bid slams without asking for aces usually have voids. South's king of hearts looks like a singleton but it does not have to be.  If South has the KJ of hearts, playing the king would be a good falsecard which, in fact, it turned out to be.

If South has a singleton heart, is there any rush to take the ♦A? - No, the diamond can only run away if South has 7 clubs in a 4117 shape.  That is hardly consistent with the bidding and in any case that hand would give partner 5 trumps so the contract could never make.  The situation you need to cater for is where West has a singleton heart, and the correct defence is to return a heart at trick 2.