Figure 2.1.7.4[Black to move]

Nxd4 looks implausible for Black because it loses a knight for a pawn. But the implications of the move change when you see that it is a fork, attacking the knight on e2 and the queen at f5. For then you see the real question is whether White's knight can be replaced with a working target. It can: Black plays 1. … QxN+; 2. KxQ, Nxd4+, winning back the queen with the net gain of a pawn after White recaptures RxN. Like many of these positions, this one can be solved as well by having a look at the consequences of any checks you can give. Black’s queen can deliver check in four ways; one of them, QxN, moves the king into a new position in which the fork might be seen if it wasn’t already.