Figure[White to move]

More on Mate Threats: Vertical and Horizontal Patterns.

Find the kernel of a discovery for White. His knight masks his queen on the e-file; this formation of three pieces on a line should be instinctively visible. White needs to vacate the knight from e5 in a sufficiently threatening manner to allow him to play QxQ a move later, which likely means he needs the knight to threaten Black’s king. The knight can’t give check, but it can move into the king’s vicinity; and the bishop on g3 is aimed that way, too. Indeed, when the e5 knight moves, it will discover an attack by the bishop on both of the king’s flight squares. Nxc6 thus puts tremendous pressure on the king’s position. It is just as effective a distraction as a check would be, because if Black does anything to save his queen White plays Nxa7# on his next turn. (He also threatens mate with NxQ, or any other move of the knight to e7.) So instead Black fends off the mate threat and loses his queen, which is loose, presently.

We might as well sketch Black's actual play in reply to 1. Nxc6, which can get a bit complicated. Black's best move is Bxb2+. You might expect White to reply KxB, but no: that would allow Black to play Qf6+ next move, using the priority of check to remove his queen from danger. Instead White replies to Bxb2 by simply moving his king to b1. Now Black plays BxN to defuse the mate threat, and White has the move he has been waiting for: QxQ. Or instead of BxN, Black could play his queen to a3; there it seems to be out of danger, and it guards both mating squares: a7 and e7. But then White simply goes ahead with Ne7+, which requires Black to capture the knight by playing QxN. Again, White now has QxQ.