The answer is 1...Rg3!! you see if 1...Qc6 then 2 Qg4 stops the checkmate but after the move played theyre are only two good moves 2 Rd1 then 2...Rxg2+ 3 Kf1 Rxf2+ 4 Ke1 Qxe5+ is terminal- and the other reply is 2 hxg3 but after 2...Qc6 now 3 Qg4 no longer works so mate is unavoidable.