When Knights Attack!

Here is a great problem I came across the other day. It is black to move.










The key is the e3 square. It would be a nasty hot spot for any one of the black knights -- forking the c2 Queen and the d1 rook. The only piece up to guarding this key square is the f2 bishop. Thus, the key is driving that lone guard away.

1... Ng4! accomplishes just this. White must now move the f2 bishop or risk the very fork mentioned above (2. exf5 looks good but is not. 2... Nxf2 now forks both of white's rook and will lose the exchange -- white will lose a rook and a bishop for two of black's knights.). 2. Bg1 is the only move where the bishop can still guard e3.

But then black has the powerful 2... Nfe3 forking the white queen and rook. The futile 3. Bxe3 is met by 3... Nxe3 leaving white with the same devestating fork.