Solution
1… Nf3! threatens Qxh2# and proves that the g2-pawn is overloaded in that it cannot defend the f3-square AND protect the h2-pawn (by blocking the line of the black rook, ie. after black plays Rd2)
1… Nf3 2. gxf3 Rd2 (threatening Qxh2#) and white cannot prevent an eventual checkmate.