Figure[Black to move]

Find the discovery for Black. The most promising kernel is on the long diagonal where his knight masks his queen, but it's no good because the rook on d4 is protected. So Black plays with other moves; he looks for any checks he might give and finds Nf3, forking White’s king and rook. If White defends with g2xNf3, he opens a line to his king on the g-file—an interesting result. Consider whether the move gives Black any new checks and you find Qg6+. It forces White's king onto h1—and (the key point to see) slides Black's queen onto line with its knight and White’s queen, creating a new kernel of a discovery. With the king moved to h1, the knight on e4 can give check, and unmask a discovery, with Ng3. After White takes Black’s knight, as he must, Black plays QxQ.

White doesn’t have to defend against the initial knight check with 2. g2xN, of course. He can play 2. Kh1. Then Black wins the exchange and a pawn with 2. …NxR; 3. e3xNd4, Qxd4.