While working with the Department of Justice to nail Mafia mobster Goratti, detective Flint is cornered and run over by a train. Arriving in the Unknown, or the after-life, he finds that there is a long wait before he can be judged as to his final destination. Thus, Flint asks the grim reaper if, in the meantime, he can return to earth and continue his war against crime. The grim reaper, himself a victim of Goratti, somehow, agrees and even gives him a costume that "will strike fear into their hearts."
As Nemesis, Flint tracks down the Mafia boss and slugs him into the flaming exhaust of a rocket, an event that so delights the grim reaper that he appoints Nemesis the permanent guardian of earth.
When he is not on earth fighting crime, or visiting his mortal girlfriend Lita Revelli Craig, Nemesis dwells in the Unknown in a lofty tower in which he keeps an apartment.
As Nemesis, Flint not only possesses super strength but can fly, become invisible, appear and disappear at will, communicate through ESP, travel through time, and grow to giant size.
However, despite being dead, Nemesis can be drowned, burned, and rendered unconscious by certain gases and poison, as well as be deprived of all of his powers if a strong light causes him to cast a reflection.