Bishop (Charles Bronson) and McKenna (Jan-Michael Vincent) escape from all their pursuers, and get back to Bishop's home, where McKenna betrays and poisons Bishop.
As Bishop is dying, he asks McKenna if this was about revenge for Bishop's earlier murder of McKenna's father. It wasn't- McKenna had no idea that Bishop was responsible for that, and McKenna never cared about his father anyway. Rather, McKenna saw a chance to ingratiate himself with the Mob by killing Bishop for them. He plans to take over Bishop's assassination business.
After Bishop dies, McKenna decides to go for a spin in Bishop's sports car. When he gets into the car, he sees a note from Bishop. The note says Bishop suspected all along that McKenna would betray him, and that Bishop had planted a bomb in the car.
The car explodes, killing McKenna.