By Eddie Kantar 
Courtesy of KantarBridge.com
Both vulnerable, IMPs.
Opening lead: ♦Q
In spite of your opening 1♦ bid, West leads your suit. East plays the ♦7. Plan the play.
Solution
With eight top tricks outside of hearts, the suit you must develop, you need to play hearts to your best advantage for four tricks. The best play with this combination is to lead low from dummy and insert the nine. You score four heart tricks anytime the suit breaks 3-3 or East has Jx, Qx, or QJxx; not a bad parlay.
The full deal:
THE BOTTOM LINE
After partner makes an invitational raise to 4NT, a new suit by the opener is natural, not some sort of response to a non-existent Blackwood bid.
At notrump, count your sure tricks outside of the suit you must develop so you will know how many tricks you need in your main suit.
With K10xxx facing A9 doubleton the best play for four tricks is to lead low to the nine. Similarly, with A10xxx facing K9 doubleton the best play for four tricks is to lead low to the nine.