Sitting West, what is your lead?
It had better be the ace of diamonds if you want to defeat three notrump.
On any other lead, declarer can drive out the K and take at least nine tricks. The lead of the A enables you to continue diamonds with profit and the contract goes four down whe partner returns a spade upon winning the K.
Because partner figures to have very little, doesn't every other lead look far too optimistic? And what's more important, South will not have gotten away with that enterprising 3NT bid and will think twice before trying to steal from you next time, you tiger you.
Bridge Today, Sep-Oct 1992, p. 32 Eric Kokish