This deal is from an EBU online duplicate
You lead the nine of diamonds against four hearts.
Declarer wins in hand with the king, partner playing the seven.
Declarer now plays the ten of clubs to the king, ace and two.
Declarer now plays the spade off table to partner's queen, which shows a holding of QJ10x(x), the king and your ace.
What do you play now?
Scroll down when you have decided.
You need to stop declarer from ruffing two spades in dummy.
It looks as though declarer has a heart holding headed by the ace and king to justify his opening bid.
If you switch to a low heart, if declarer guesses right and plays the jack then he has one spade ruff, five hearts, two diamonds and two club tricks.
However, if partner has 10xx of hearts a switch to the heart queen will beat the contract as partner will get a heart trick if declarer ruffs a spade with the jack of hearts.
The full deal was