Look at this puzzle:
[FEN "r3q3/1pb1rbk1/2pn1p1p/p1Qp1Bp1/3P4/4P1NP/PP3PPB/3RR1K1 b - - 0 1"]
The aim of the puzzle is: Black to play and attain a good position. But I can't find a good position here. Then I looked at the solution, which was 1... Nc4!! . But I can't understand what happens after this move. I think both sides are equal. Can anyone help me?