3 hands remain and you are 15 behind and along comes this one. After the jump to 3!D the S hand paused for some time before re-bidding S and you find yourself on lead. The good news is declarer will not be able to establish D without allowing you to get in. The bad news is evident, you have no promissing 5 card suit and C are so weak they offer little hope, at least that is my view.
Here was the bidding, with you in first seat contributing the first pass.
P P P 1D
P 1S P 3D
P 3S*P 3N * represents a pause for the cause.
Now you are faced with finding your lead. Without giving away the ship it strikes me you can safely rule out leading a D. Lets face it, partner is not going to be looking at a very good hand.
Consider that a H lead could possibly give up timing. I feel that you are unlikely to find partner with more than the hope of 1 entry really. But at least they can attack H from that side of the table and you will not give up a tempo. So after some thought you elect to lead the J of S, fully prepared to say "sorry partner I was a mental midget".
Look what happened. Declarer of course covered with the K partner wins the A while declarer shows out dumping a C. Now from partners view it is highly likely you have a 5 card H suit that looked dangerous to lead from, so they make the best return of the 9H. Declarer plays the 10, you win A and continue S. How can this be wrong really. The delcarer has no chance any more, if he wins you will later collect 2 more S tricks. He tries the 9 losing to the 10 and the 8H comes back. We see the J and cover, he wins K, cashs a S dumping a H and tries the D hook. Wow, 2 down out of no where and a H lead gives away the contract easily.
The rest of the story comes in part 2. However, lets see how we view this opening lead. Would or should we have led H as a better hope? Was the J of S sensible in anyones view?

Help
