
Solution

1… Nxc3 2. Qxc3 Qxb1
The point of 1… Nc3 is that is forks the two white rooks, discovers the attack of the black queen on the b1-rook and at the same time draws the white queen away from defending the b1-rook.
1… Nxc3 2. Qxc3 Qxb1
The point of 1… Nc3 is that is forks the two white rooks, discovers the attack of the black queen on the b1-rook and at the same time draws the white queen away from defending the b1-rook.