Another critical moment in the 1978 Irish championship came in round 3, when Alan Ludgate had Black against Adrian McDaid. In a complex struggle, chances were around equal until quite late on, when an error from McDaid caused his position to collapse quickly.
30. ?
The diagrammed position arose half a dozen moves from the end. The game continuation 30. Be1 (not yet the fatal error) was met with 30… Qb4, and afterwards Ludgate’s notes suggested, plausibly enough, that 30. Ra4 would be better, and should hold.
In fact, though, 30. Ra4? would transform a position that is almost equal into one that is dead lost. The refutation is not at all obvious, at least to me; in particular it is not at all evident why it is so deadly.
I’ll leave this as a puzzle: how does Black refute 30. Ra4? See the game for the solution.