[whereagles]

Take club, ♠A, ♦T.

That should avoid embarassments when declarer has 3 clubs and/or pard fails to play a spade after cashing out the diamonds.

[FrancesHinden]

I would win the club and try and cash diamonds.
I probably play back my original 4th highest diamond, rather than the 10, but I might want to have a closer look at my pips first.

The probability of partner's card being a singleton or doubleton depends on exactly which pip he plays (the 7 is a singleton or 78 doubleton; the 6 is a singleton or 67 or 68 and so forth).

The difficulty is that you simply can't think for long about this. You can think briefly at trick one, but if you think for a long time declarer may guess that is your problem and cash the CA on the second round anyway (hoping that the SK is an entry as an alternative to the clubs coming in)

[mikeh]

Assuming that partner led 4th best, the ♦10 back can hardly cost and may be needed: give declarer KJ32 and if my spots are 54 (or equivalent spot distribution) and he ducks my 4 and now partner has to guess which major to play.

As for the ♣ suit, one may ask why declarer did not lead 8 from 8xx or 8x. But that is a red herring. If he has 8xx, low to the dummy makes sense because he can hardly lack communication in both reds and he might get you thinking too deeply into the hand with Kx, as indeed we are tempted to do here.

Maybe partner played low from xx, either without thought or for some deceptive purpose or to tell you to play ♦s or whatever... but if he holds a stiff ♣, then we need to win for obvious reasons... and we can be reasonably confident that we need to play a ♦, since on this auction, he probably wouldn't lead a ♦ from a weak, one entry hand with Jxxxx (at best) and a side 4 card major.

So win the K, cash the ♠A, to prevent catastrophe when ♦ are 4-4 and partner leads a ♥.. and table the ♦10.

I suspect I've missed something, since this seemed relatively easy

[Apollo81]

i'll also jump on the ♣K, ♠A, ♦10 bandwagon