Mate in 3

With d4 and g7 under its watch, the a7 queen is Black’s key defender. If it concedes either square, White lands an immediate mate with Nd4 or Nxg7. The straightforward attempt to shield the queen with the c6 rook doesn’t work: 

1.Rb6?, threatening 2.Nd4#, is refuted by 1…Ra4!

Instead, the solution begins with the subtle 1.Rd6!, setting up the threat of 2.Rxd5+ Kxe6 3.Nf4#. If now Black defends with 1…b4, then White goes 2.Rb6!, threatening 3.Nd4#. Black has no way to prevent this without allowing 3.Nxg7#. Thanks to the b4 pawn, Black's rook can no longer guard d4.

And if Black tries 1...Nd3, White responds with the striking 2.Rd7!, threatening 3.Nxg7#. This results in 2...Kxe6 3.Bg4#, 2...Qd4+ 3.Nxd4#, or 2...Qxd7 3.Nd4#.

A masterful illustration of the Focal theme!