1.Bg5 with the short threat 2.e4. In two variations the black knight interferes with a rook.
White first drives the king away to unpin the e6 rook, then decoys the rook to open a bishop guard on f5 in
preparation for a switchback mate. 1...Sc5 2.Rd5+ Ke4 3.Sf6+ Rxf6 4.Rd4 and
1...Sd6 2.Se7+ Ke5 3.Bf6+ Rxf6 4.Sc6.