QJ3, JT642, QJ2, Q2
North is dealer. The bidding goes.
(Pass) - 2S by pard - (X) - Pass by you
3C - Pass - Pass - 3S
Pass - Pass - 4C - All pass.
Pard leads the ♠A (from AK) and you see:
(Note you are west, dummy is South, at the bottom)
After winning ♠A, partner switches to the ♦5 (presumably singleton). dummy plays low ♦, you put in the J, declarer (North) wins the K.
Declarer then plays a ♣ to A, heart to A, and takes a losing finesse to your ♣Q while pard follows.
Handviewer link: http://www.bridgebase.com/tools/handviewer...3h2hah7c5c6c9cq
Now what?
(As usual adv/+ please refrain from posting spoilers too soon)

Help

Lead ♠A by East.