1. Rc5-c4 (threatening both Nd7-c5# and Rc4-b4#)
(1. Rc5-b5+ would fail to 1. ...Kb3-a4)

Black now has several possible moves, which can be categorized as follows:

• Black takes the Rook, or covers the b4 square:
  • 1. ... Nd6xc4
  • 1. ... d5xc4
  • 1. ... Na7-c6
  • 1. ... c7-c5
  
  White has the same winning move in each case:
  
  • 2. Nd7-c5#


• Black covers the c5 square:
  • 1. ... b7-c6
  • 2. Rc4-b4#