You hold: ♠AKQJ65 ♥AQ7 ♦A92 ♣5 and RHO passes. This is a 4 loser hand, despite having only 20 HCP so you open 2♣. It goes DOUBLE on your left and partner passes. This partner plays controls over 2♣, so you know partner has NO Aces and probably no Kings. (2♦ would have shown no Aces and 0 or 1 King, so the failure to bid 2♦ makes it unlikely you'll find a King opposite your hand.) However, duplicate was not made for wimps, so you bid 4♠ anyway (with apologies ready for partner if you go down).
LHO leads the ♣A, promising the ♣K, and you are looking at:
♠1042 ♥J83 ♦1054 ♣10874
♠AKQJ65 ♥AQ7 ♦A92 ♣5
It looks like you are going to need that apology. Unless you find the miracle holding of ♥Kx in hearts on your right, you are slated to lose one club, two diamonds, and one heart. [Remember, playing the ♥J from Dummy will only promote an opponent's ♥10 even if RHO has the ♥K.] RHO plays the ♣9.
LHO falls from grace by continuing with a high club and the ♣Q falls on your right as you ruff with the ♠J—to preserve a low spade for getting to Dummy. Things have just gotten interesting! (LHO has NO reason to play second top club. Can count and see that the ONLY outstanding club is the Queen—after trick one—so can continue with a LOW club since either partner has the Queen, or I have the Queen and his partner is ruffing.)** The ♣108 remaining on dummy are now threat cards. If LHO plays another club, I will get a club trick.
So, before I put all my eggs in the heart King basket, I play two top spades. Spades are 2-2. Yay! So, now I play a low diamond. LHO eyes it suspiciously and goes up with the ♦K (looking like someone with a doubleton King). He cannot return a club without giving me a trick and does not want to risk a heart, so he returns a second diamond. RHO plays the ♦J and I take the ♦A and exit with a diamond. As expected. LHO shows out (discarding a club) and RHO wins the trick.
If the ♥K is on my right, I am home free—and it no longer has to be doubleton. RHO cannot lead a club because he does not have any more. He cannot lead a spade because he does not have any more. If he leads a diamond (having started with 5 of them), it will be a ruff-and-sluff and I will ruff in dummy, discarding a heart from my hand and FINALLY try the heart finesse. If RHO leads a heart, I will let it ride to the ♥J in Dummy. (That is what RHO elects to do.) My over-bidding is justified as the ♥J wins in Dummy and I take the marked heart finesse a second time.
**FOOTNOTE for more advanced players: The BEST defense by LHO is to play a SPADE at Trick two. Here is the reasoning. With balanced Dummies, end plays are the danger. When end plays are a possibility, you want to keep as many of your safe exit cards as possible. It is unlikely I have two clubs on this auction, so a second club removes both LHO's safe exit card, but also his partner's safe exit card in clubs. (The club threat in dummy is not as important as me being able to strip RHO of his clubs, spades, and safe diamond exit cards.) Even if LHO continues with a LOW club at trick two, the damage has still been done. I can ruff (high); pull two rounds of spades; duck a diamond; win the ♦A and exit with a diamond and the end play still functions. LHO should expect a spade lead to be 100% safe because I have jumped to game on my own, so MUST have a 6 or 7 card solid suit; LHO has two spades; dummy has three spades. Therefore, LHO's partner cannot have more than two spades. Even if RHO has the Queen [highly unlikely on this auction], it would fall anyway.
Double Dummy: If I KNOW that RHO has only two clubs and spades are 2-2, then double-dummy even ONE top club lead is too many. LHO shifts to a spade. I take second round on dummy and ruff a second round of clubs and again eliminate diamonds as before. VOILA. [If anyone played it this way, I would hold my cards closer to my chest. Sane Declarers will hope for ♥Kx on right.]