To succeed, you require focus...
Your opponents bid 1D - 1NT - 3NT.
Your partner leads 3s
This is what you see:
3s led H 9742
You know that declarer holds a weak hand with no 4-card major suit.
When declarer plays low from dummy, which spade will you play, and why?
What is your overall plan to try to defeat 3NT?
Are you focused?
Let's think it through together...
With dummy holding 2s, you know that partner has led her lowest spade and therefore holds no more than four of them.
Declarer's play of a low spade from dummy is very revealing.
If he held nothing in spades, he would rise with Qs; similarly, if he held As, he would rise with Qs. Playing low suggests that he holds sJxx.
So South will make a spade trick whatever you do.
Look at the strong dummy and count declarer's tricks: 3 hearts, 5 diamonds and, sooner or later, the spade trick. That is 9 tricks.
This accepted, you must think of a way to make 5 tricks pretty quickly - at least by the time you take your Kd.
You have Kd and two spade tricks, so you must establish two club tricks for your side. You cannot afford to play low on the first trick, so win with Ks, and switch to a club immediately. It is vital that you push any high cards South may hold into the waiting jaws of your partner's assumed decent clubs. To this end, you must lead 10c.
Whether South plays Ac or Qc, or even low, nothing can stop West from setting up two club tricks and, when you win your Kd, you can lead a second (or third) club to West and defeat the contract.
Even if West did not hold 9c, if declarer plays low, West could win and switch back to spades; if declarer plays Ac, then two club tricks can be taken the next time you lead one.
Did you get it right? Did you take your time? Were you focused?
S A973 S K1054
H 1065 H 9742
D 63 D K8
C KJ93 C 1052