Correct answer: Nc51.Nf8?? (2.Q:e7#) 1...K:f8 2.Q:h8# but 1...g4! 1.N:g5?? (2.Q:e7#) 1...Kf8 2.Q:h8# 1...O-O 2.Qg7# but 1...Q:g5! 1.Ng7+??
