The lead was the club jack, and South won with the king.

Now South had to guess the location of the club jack.

West shifted to the club jack, and South won with the king.

If South takes that on the board, he must continue with specifically the club jack.

Then he continued with the club jack and there was no defense.

He then led the club jack, and this won when West did not cover.

The club jack was led and held the first trick.

So West was not tempted to lead the club jack.

The lead of the club jack was the best the defense could do.

South led his club jack, leaving West with no winning play.