Fincher and Walker spent six weeks changing the tone and trying to make the story work .
Fincher liked the various plot twists but brought in Andrew Kevin Walker , who had worked with him on Seven , to make the character of Nicholas more cynical in nature .
Fincher and Andrew Kevin Walker spent six weeks changing the tone and trying to make the story work .
Fincher liked the various plot twists but brought in Andrew Kevin Walker , who had worked with him on Seven , to make the character of Nicholas more cynical in nature .