BIDDING & DEFENSE
RHO opens 2♠ and your hand is ♠A62 ♥K84 ♦KQ4 ♣A1073. Yes, you are not thrilled with your single stopper in spades, but bid 2NT. That is the correct bid: 15-18 HCP and at least one spade stopper. That will allow your partner (with 10 HCP) to make a Stayman inquiry and then put you in 3NT.
♠8 ♥Q1062 ♦A532 ♣KJ65
♠A62 ♥K84 ♦KQ4 ♣A1073
You duck TWO rounds of spades, cutting communication between the opponents. Then play the ♣K and run the ♣J toward your hand— an AVOIDANCE play to make sure RHO cannot get in again. When LHO's the ♣8 falls and RHO covers with the ♣Q, you kill it with the ♣A. Now you can afford to play two top diamonds from your hand. RHO will play ♦7 then ♦J. It appears RHO has a singleton heart, so play the ♥K. LHO will take ♥A and play the ♦10 as RHO shows out. Finesse RHO for the ♣9. You end up with four clubs tricks; three diamonds; one spade and TWO hearts when you finesse LHO for the ♥J.
If you double instead of bidding 2NT, you will regret it. You will hear 3♠ on your left and partner may pass and there you are. When you defend 3♠, you lead the ♦K and this dummy comes down:
♠1075 ♥AJ973 ♦10986 ♣8
♠A62 ♥K84 ♦KQ4 ♣A1073
Partner signals encouragement in diamonds, but there is no reason to continue the suit. Do NOT panic about the 5-card heart suit in dummy. The odds are very high that Declarer does NOT hold EXACTLY ♥Q10x or ♥Q10. Dummy's best other asset is the singleton club. Lead a LOW spade at trick two, maintaining control of the suit. Then, when Declarer plays a low club to his ♣9, take your ♣10 and lead the ♠A and your last spade. Declarer will take only five spade tricks and one heart trick on this defense—down 3. If you panic and start cashing top tricks, you allow Declarer to escape for down 1 or even make the contract.
Incidentally, for the person holding the 10 HCP, if your partner DOES double and your RHO raises to 3♠, YOUR BID is a Responsive Double—NOT pass. That gives you a chance to get to game. And if partner declines to bid 3NT and simply passes and leads a diamond and shifts to a spade, you'll get 800 instead of your 630 for 3NT making 4.