Acol weak NT system. The displayed auction may not be correct. I know partner raised diamonds at some point and North definitely had the last bid, I can't remember whether or not partner doubled before raising.
Partner leads the ♦A. I wanted partner to switch to a heart and came up with the idea that this was similar to the situation where dummy comes down with a singleton and the rank of the card played signals which suit to switch too. I knew declarer almost certainly a singleton and thought partner would deduce this, so played the king in an attempt to induce a heart switch.
Partner did switch, unfortunately she switched to a club straight into declarer's AQ. That was 5♠= for a bottom instead of 5♠-1 for a top. Oops.