West   North   East   South
                                 1♥
pass    1NT¹     2♠     3♥
pass    4♥         all pass

1 - forcing one round

North-South reach 4♥ after you overcall in spades. Partner leads the ♠10, you overtake this with the jack and cash the ♠A. When you play the ♠K, declarer ruffs this with the ♥K, partner discards a club. Declarer now crosses over to dummy with a club, and plays the ♥8. Your move.

Solution:
You have 13 points in your hand, and dummy has 12. Declarer opened the bidding and then took a free call at the three-level, and therefore should have a good hand. You cannot expect any help from partner in terms of high cards. However, partner may be able to provide you with some help in the trump suit.

Your right play is to duck the first trump. Declarer wins the trick with the Queen, and plays a low heart to the eight, you win the ace perforce. Now you play a spade through declarer, promoting partner's ♥7 as the setting trick.

If you win the first heart with the ace and shoot back a spade, dummy's trump will counter any threat of a trump promotion.

Analysis:
Bridge Baron's double dummy solver tells us that 4♥ can be made. This is a complicated line however, and is extremely tough to execute in practice. Here is one winning line of play (other minor variations are possible). After ruffing the spade return with the ♥K at trick three with West discarding a club, declarer crosses to dummy with the ♦K, and plays a heart to the ten and queen. He now cashes the ♣A, plays a club to the King, and ruffs a club. He now plays the ♦A, and plays a diamond to the queen. East cannot profitably ruff this trick with the ♥A; ♥K will take care of any spade play from East, so he discards. Declarer plays the last diamond from dummy (East discards again for the same reason) and ruffs in hand. Now declarer simply leads a heart to the nine, and takes his tenth trick with the ♥J.
Par Contract Analysis:
The par contract is 4♥ by North-South.

Bridge Baron deal No : N4405-97742-85848-08926-06255-48962