Jennbridge: What contract?

I opened this 14-16 NT hand the other night in a local team game and partner bid 2♥, a transfer to spades.

♠8xx
♥KQJx
♦ xxx
♣AKJ

After I bid 2♠, he then bid 3♦, a forcing bid showing spades and diamonds.  What is my call?

*****************

Although it is usually right to play in your 8-card fit (spades), in this case I had plenty of reasons to rethink conventional wisdom:

• My hand was perfectly balanced with no ruffing values 
• All of my values were in the unbid suits--hearts and clubs
• Partner's values were in spades and diamonds--so all suits should be well-stopped.

With all this in mind I bid 3NT and received a club lead.

♠KQ9xx
♥x
♦ AQJxx
♣109

♠8xx
♥KQJx
♦ xxx
♣AKJ

I won in my hand and took the diamond finesse which lost.  A club was returned and I played another diamond (all following) to check on the suit break before leading a heart to my king, losing to the ace on my left.  LHO gave it best defense by putting me back on the board with a diamond (rather than conceding the contract by putting me back in my hand to cash winners).

After I played the diamonds I exited with the spade king, won the queen, and when I exited with the last spade they had to put me in my hand for the 9th trick.  I wasn't particularly worried about a 4-1 spade break because there would have been various endplay opportunities.

All in all, it was a fairly routine hand, but as we were sorting our hands for the next board, we all realized that  in a spade contract there were 4 losers:  2 spades, 1 diamond and the ace of hearts.  If our opponents played in 4 spades we would have a substantial gain.

Sure enough, when we compared scores we won 12 IMPs as we were plus 600 and our teammates were plus 100 against 4 spades.

See you at the table!