Too often defenders panic, thinking their tricks will somehow vanish. Keeping count will keep you on track.
Your partner opens 1♣; RHO bids 1♥; and you negative double with ♠10654 ♥J8 ♦A10983 ♣964. Now, some of you may NOT negative double with this hand as you only have 4 working points, but I encourage my partners to be aggressive with the spade suit and tell them it is OK to bid with only an Ace in your hand because it is a sure trick and an entry and you could have 6 random useless points and bid. Anyway, LHO bids 2♣, showing Limit Raise or better of partner's overcall. Partner now bids 2♠ and RHO bids 3♦ (help suit game try in diamonds except opponents have a bidding misunderstanding and LHO thought 2♣ was LR or better and RHO thought 2♣ was a transfer to diamonds.) Anyway, opponents stop in 3♥.
You lead fourth best spade and Dummy hits with: ♠A9 ♥Q62 ♦KJ54 ♣Q853 Declarer ducks and partner takes the ♠K and plays the ♣K. (From ♣KQx OR ♣AKx in middle of the hand) Your duty, with ♣Q in dummy, is to give count, so you play the ♣4 and partner returns the ♠2. Declarer takes the ♠A and leads a low club from dummy and ruffs it. Then Declarer cashes top two hearts and the ♠Q. Now, a low diamond comes from the hidden hand.
Have you been counting? Declarer started with six hearts—because she pulled only two rounds and stopped. Declarer is known to have a singleton club because she ruffed the second round of clubs. Declarer is known to have exactly three spades. (She played three spades and your partner bid 2♠ opposite your negative double, so partner has exactly four spades.) 6+1+3 = 10. Ergo Declarer has three diamonds which means your ♦A canNOT go away, and partner has two diamonds. However, if your partner has the ♦Q, which is likely for her opening bid, that card could will get trashed by the ♦K on the second round if you hop with your ♦A. So duck smoothly on the first round.
Of course, Declarer should be counting HCP and play YOU for the ♦A and play the ♦K and then a low diamond. When your partner is forced to win the ♦Q, she will be end played. She will have to either play a spade for a ruff and sluff or play another top club which declarer can ruff, setting up ♣Q in dummy with the ♥Q remaining as an entry.