Initially Peter Creedy hires him and his men to temporarily bolster the police force after V destroys the government's surveillance equipment, but Helen Heyer recruits him to her side to ensure Creedy's downfall by offering to place him in charge of the Finger after Conrad Heyer comes to power. He temporarily becomes Helen's lover.
After Creedy's takeover, Harper fulfills his end of the bargain with Helen and kills Creedy with a lethal slash from his straight razor. Conrad beats Harper to death with a wrench as he fatally slices his neck.
Another information can be added about Harper. He was the one who had sold a gun to Rosemary, the "rose" that had killed the leader Susan.