Playing in a club game against an expert defender, we are in 4H. I get the lead of the 9 of diamonds (top of nothing) and dummy hits with 7 diamonds. I play the queen to the Ace of diamonds and get a low diamond lead back. How do you play? (Click on "South" to hide the other hands. Then, click on Next to see the opening lead and dummy.).
At the table, I discarded a low club and when west played low, I saw that dummy's diamonds had been established. I led a heart to my King of hearts and played the queen of hearts to discover the bad news. Now, west had a trump and I had at most one discard on the diamond. I finessed the spades, but it lost and soon I found myself down 2.
Did you also get led down the garden path, or did you find the line to make? I think it goes to the reality distortion field that a good defender can create that I didn't see the line to make the contract until I drove all the way home from the game.
If you keep clicking Next on the above diagram, you'll see how to make it. It involves realizing a couple of things. First, the low diamond return is a dead give-away that east has the Ace of clubs. With two aces, he can hardly have the king of spades also. He is not worried about setting up diamonds, so his partner probably has 4 trumps and if so, the right line is to forget the fully set up diamonds (the diamond suit is the garden path he's leading you toward) and take a ruffing finesse.
UPDATE: Corrected play in response to first comment.