As West, you hold:
Partner opens 1 and the opponents reach 4 as shown below. What is your opening lead?
Partner wins the first trick as shown...
What do you know about the spade suit?
Partner has AQ10xx.
Partner has KQxxx.
Partner has KQ10xx or AKQ10x (or longer).
At trick two, partner takes the A (confirming that he started with AKQ). All follow suit.
Then, he plays the K as shown below. What do you play on this trick?
Partner gets the message and plays a fourth spade as shown:
What will the result be?
4 making 4.
4 down 1.