The bidding: A weak-two bid can be a most effective pre-emptive and descriptive bid. In third seat, because partner is a passed hand, one can break the rules of a weak two. Even five card suits can be opened with a weak two. Here the diamond suit is too poor in quality to open either vulnerable or in second seat. Having control of the trump suit is missing but with three cards in the majors, being disruptive is much more important.
South overcalls 2NT. This shows a strong notrump opener of 15 to 17 points and two diamond stoppers. Three cards to the ace are also good because declarer can hold-up twice, likely depleting the suit from West’s hand.
Had East passed, South would have opened one notrump.
It should be noted that 2NT over a weak two is not showing a two-suited hand. Had East opened a suit at the one level, 2NT shows 5-5 in the two lower unbid suits and usually a weak hand. That bid is not used because a weak bid is not done over opponent’s weak bids. Preempting a preempt is usually not done.
If South had poor diamonds, South could have opted for a double. With four-four in the majors, a double would have been the safest bid, although 2NT is much more descriptive.
North transfers to spades and rebids 3NT because he has five spades and game going values. With six spades, he would have bid four spades not 3NT.
The contract: Four spades by South
The opening lead: The jack of hearts
Although East did not double the alerted transfer bid of three hearts for a heart lead, the jack of hearts is the safest lead. East made a third seat weak two so leading the king of diamonds is not wise. Leading the ace of clubs may just set up declarer’s club suit because the king is likely with South.
Furthermore, West does not have a trump stopper so it is not wise leading a doubleton. It would have worked here, but West still should heed the warning that partner’s preempt gives. “Partner, I am weak.” Without nothing better to lead, the king of diamonds could be led.
The play: South wins the opening lead and draws two rounds of trump. Declarer often stops when he discovers a bad break. If he draws four rounds of trump, there is a risk, East or West will gain control and run his suit. Here it is safest to draw trump and attack clubs because North and South have three heart stoppers and two diamond stoppers in the ace and ruffs. West wins the ace and continues hearts. South knocks out the king of clubs and claims eleven tricks.
Had West made the risky lead of the ace of clubs, he would have kept the contract to ten tricks.
The result: Four spades making five for +450