What's the Best Move? (II)

Black to Move

From Kernighan - Tomkovich, Rd. 4 of the Kenilworth CC Championship. Black, a B-player, can beat a Master if he finds the shot (and the follow-up).

From the great Kenilworthian blog. I'll admit I didn't find it, but I learned something through my failure.

Don't look at the annotated game here until you know the answer!