Dealer: East Vuln: E/W

Initially, we are taught third person plays high unless you need to keep your honour over dummy, but ... (not always)

Partner has led from his club suit despite Clubs being bid and has not been put off doing so.

Surely partner would only do this with at least a five card suit. Therefore partner must have KJ10XX in clubs or J10XXX and that would mean declarer has a singleton Club King. Therefore our only hope to muster five defensive tricks it to play that Ace.

When you do so the King falls from declarers' hand and you now play back a club and now you will eventually muster 4 Club tricks and a Heart or Spade.

Declarer wins the second Club and runs off 6 Diamond winners. He might now try a Spade which partner wins and cashes 3 more club tricks.

At trick 3 declarer whilst in dummy might try the Heart finesse which fails and partner can then instead cash  3 club winners at that point and the Spade Ace  instead now defeating the contract by Two..

(NB Perhaps South, the hog, might have given delayed 3 card support instead  and now NS get to the unbeatable  4♠  contract losing just 1 Spade, and 1 Club and 1Heart)