Mate in 3

The key is the subtle yet deadly 1.Qd8!, aiming for 2.Nb2+ Kc3 3.Qxf6#. Black has two main defences worth noting: 1...g4 and 1...Ng4, both of which guard the crucial f6 square.

1…g4 is met with 2.Re7!, threatening 3.Rc7#. Now, if 2…Kc5/b4, 3.Rxe4 mates. Similarly, 1…Ng4 is answered by 2.Rd6!, threatening 3.Rd4#. Yet again, the black king can flee to b4 or c5, only to run into 3.Rd4# anyway.

The second move in each variation self-interferes with the f8 bishop, paradoxically granting flight squares to the enemy king — tricky!

Of course, 1...Nf3 is a third option for Black, but this is easily countered: 2.Rxe4+ Nd4 and 3.Rxd4 or 3.Qxd4 mates.