The contract is now a sure thing. Draw three rounds of trumps. Only East can hold diamond length and you can cater for him having all 5 missing diamonds. Play the ♦10 towards dummy. If West shows out, duck the trick to East. If East wins, you later have a ruffing finesse against him. If he ducks, you can later ruff a diamond and concede just one trick in the suit. Anything less than a 5-0 diamond split makes your task easier. You can also succeed by leading the ♦2 towards dummy provided you rise with the Ace when West shows out.  A small diamond towards your ten places East in the same dilemma as before.

You plan to return partners suit. It looks like East has led from ♦Qxxx. If you win the first club with the Knave, South will have no option but to enter dummy with a spade and take a winning heart finesse for his contract. If you win with the King, declarer might decide that he should play on clubs for his contract rather than risk a heart finesse. If he does play this way, you will defeat him with 3 clubs and 2 diamonds. 

This hand hinges on the heart suit. If you needed 3 tricks from hearts, your next play should be a heart to the King. On this hand however, you only need 2 tricks in hearts to fulfill your contract and the correct play is to now run the ♥8. If this loses to the 9, you can later set up 2 more heart winners. If you make the mistake of playing a heart to the King, you will be limited to one heart trick if the cards are as shown.

From your point of view, you don't want declarer to discard a losing heart on the fourth diamond. Whilst you don't know how the spades lie, the best defence at this point is to return the ♠K. This denies declarer an entry to dummy. At the table, declarer won the ♠A and played another spade, but West ruffed. 2 rounds of hearts followed by a third spade promoted an extra trump trick for the defence, giving them a penalty of 1400.

The contract hinges on how you play the diamonds.  You might expect East to be short in the suit as he has pre-empted in a different suit, but this is not certain.  Win the spade lead and play 1 top diamond: lets say they both follow but no Queen appears.  Now you should cash your heart and club winners in dummy and watch what East plays.  You can infer from the lead of a low spade that East has 7 spades and West 3.  When you play off your winners, you count how many clubs and hearts East held.  If he totals 3 cards in these suits, he figures to hold 3 diamonds and ultimately you will finesse the ♦J.  If East shows 4 cards, you play to drop the diamond, and with more than 4 cards in hearts and clubs, you resign yourself to failure.  Counting is the key.

6♠ is 100% once there is no trump loser - it is just a matter of counting your sure tricks. You have 6 spades, 3 diamonds, 1 heart and 1 club on top and you always have an extra trick in hearts irrespective of who has the ♥K.  Just draw 3 rounds of trumps and lead the ♥Q, throwing a diamond from dummy.  This gives you 12 tricks no matter how the opposing cards lie. The diamond suit is an illusion on this hand as you don't need to generate any extra tricks in the suit. Somehow this is not easy to see at the table.

If you look at the full deal, you will see that the diamonds break 5-0 on this hand, so 7♠ looks doomed as the King of hearts does not drop doubleton. However, this hand shows the fascination of the game in that the grand slam can still be made on the above layout. Can you see how?

Win the trump lead and test the heart suit  to see if the King falls. When it doesn't, you just run all the trumps.  East comes under pressure in 3 suits. He cannot discard 2 diamonds without immediately conceding defeat so say he bares the ♣K. You cross back to hand with the ♦A and play off 2 clubs to squeeze East again.  

It is clear that South holds ♠AQx and it is going to be impossible to beat the contract unless you can shut out dummy's diamonds.  The way to do this is to play the ♥Q, a little known blocking play.  If the Queen is covered by the King, partner must play his part and duck.  To lead a low heart instead of the Queen is not so effective.  South will let it ride round to his 10 and will subsequently enter dummy by finessing the ♥J  

Count your tricks as always.  The club lead means you have 5 spades, 2 clubs and 2 diamonds so you are on trick short.  The extra trick might come from a successful diamond finesse, or the cards might lie in such a way that you make a heart trick.  However, a little thought will show that you will always make a heart trick if the opponents lead the suit rather you you having to broach it yourself.  You should therefore draw trumps and cash your clubs before playing 3 rounds of diamonds, refusing the finesse.  Whoever wins this trick will have to open the hearts or give you a ruff and discard.

This is an example of a second degree assumption.  If you are to have any chance of making the contract, the ♦A must be with West.  If this is the case he cannot hold the ♠A - else he would have had enough to open the bidding.  Since you can only lead trumps once from dummy, you should win the heart and lead a spade, playing the King if East plays low.  You hope the full layout is akin to that shown. 

With West marked with all the missing high cards, the danger is that spades break badly.  You should therefore win the ♣A and play a spade towards dummy.  When the Jack holds, return with a diamond to play another low spade towards dummy's Queen.  All that West can do is win one spade, one heart and one club trick.

It is difficult to see declarer succeeding unless he has a solid club suit.  Since you know that as the cards lie, he cannot overtake in clubs, you must attack South's only possible entry - the ♥A.

At trick 2 switch to the ♥K and if this is ducked, continue with another heart.

If instead you play a second spade at trick 2, declarer wins, cashes dummy's clubs and returns to hand with the ♥A to take his remaining club tricks.  In the endgame you will have to concede the ninth trick.

On this hand it is all too easy to allow the first trick to run round to your hand and to win cheaply with the ♠10.  This is careless play.  If your ♠10 is forced out at trick 1, when you knock out the ♣A, West will win and play ♠ AJ.  This sets up another spade trick for when he wins the ♦A.  On the reasonabkle assumption that West hold all the missing Aces, you must play the ♠Q from dummy at trick 1.  Now West cannot attack spades again without conceding 3 tricks in the suit, bringing your total winners to 9.

If South held ♠Kxx, it would be easy to see the need to duck.  There are 2 diamond honours to knock out and this can be done safely if they are divided or if East holds both.  By ducking the first spade, declarer ensures that East will not have a spade to return when he gets in with his diamond honour.  A little thought will show that with West marked with the ♠K, the ♠QJ are effectively the same as holding the King - hence you should duck at trick 1.  If you win trick 1 and play a diamond, East can win and return his spade and West will clear the suit with a diamond entry to enjoy the established spades.  If you duck trick 1, East will return a spade, but you have 2 spade stops and now East is out of spades when he wins his diamond trick.

[If West held both diamond honours, there must have been a good chance of the hand opening the bidding]