Set Play:

 1. ... d6 [a]  2. Sa7 [A] #

Try: 1. Kd8? waiting

 1. ... d6 [a]  2. Sa7 [A] #

  But 1. ... b6 [b] !

Try: 1. Sbc7? waiting

 1. ... b6 [b]  2. Se7 [B] #

  But 1. ... d6 [a]

Try: 1. Rc3? waiting

 1. ... d6 [a]  2. Sa7 [A] #

 But 1. ...  Qxc3!

Try: 1. Rc1? waiting

 1. ... d6 [a]  2. Sa7 [A] #

 But 1. ... Qxc1!

Solution: 1. a4! waiting

 1. ... b6 [b]  2. Se7 [B] #

 1. ... d6 [a]  2. Sa7 [A] #

 1. ... Qxc4 2. Rxc4#