1… Rf2! attacks and pins the defender of the g1-square and threatens Qg1#
1… Rf2 2. Rxf2 Qg1#
White doesn’t have any good solutions to the threat of Qg1# ie. 1… Rf2 2. Ne2 Qh1+ 3. Kg3 Qxg2#
1… Rxg3 2.Kxg3 and white survives for the moment.
1… Qe1, threatening Rxg3, is also strong.