Black Friday

Red Cannon flees from four former gang members and crashes into professor George Kingsley on a city street. The collision cripples Cannon and leaves Kingsley with life-threatening brain trauma. The accident sets in motion Kingsley's peril and the radical medical intervention that follows.

Dr. Ernest Sovac performs a radical operation, transplanting part of Cannon's brain into Kingsley to save his life. Cannon dies as a result of the transplant, while Kingsley survives and begins a fragile recovery. The procedure plants the seeds for the looming dual identity.

Sovac uses hypnosis to fully awaken the Cannon identity within Kingsley's body. Cannon's presence comes with a dramatic change in appearance, making him unrecognizable as either Kingsley or Cannon. Kingsley learns Cannon's memories and the recent events since the accident.

In the Cannon persona, he hunts and strangles his former gang members. The killings resemble those of a mysterious 'gangster killer' the police cannot identify. After each act, the Kingsley persona returns, exhausted and with no memory of the killings.

Law enforcement is baffled by the killer's identity and cannot link the murders to Kingsley. The surviving gang members suspect the killer is an associate who Cannon may have told about before his death. The mystery deepens as the spree continues.

Sovac pressures Cannon, embedded in Kingsley's body, with the threat of using hypnosis to force permanent dominance. He hopes to force Cannon to reveal the hidden stash and accelerate his research. The coercion pushes the ethical boundaries of the experiment.

Kingsley's wife Margaret and Sovac's daughter Jean travel to New York out of concern for Kingsley. They want to support his recovery and protect him from the dangers around him. Jean recognizes Kingsley in the Cannon disguise and begins to piece together the truth.

Jean explains Kingsley's dilemma to Sovac and pleads to let him return home to recover. She argues for Kingsley's normal life and safety. Sovac relents, promising to return Kingsley in the morning.

That night Cannon goes to retrieve the stash of money rumored to be hidden in New York City. Sunny, Cannon's lover, has tipped off the remaining gang members who trail him to the stash. The pursuit sets up a dangerous confrontation over the fortune.

Cannon fights and strangles the remaining gang members and Sunny, securing the stash. He returns to Kingsley's body with the box, unaware that it contains Cannon's fortune. The line between Kingsley and Cannon remains blurred as he resumes life.

Back home and in his daily routine, Kingsley seems to function normally, but a police siren reawakens the Cannon persona during a class. He must confront the recurring killer within him once again. The moment signals that the internal conflict is not fully resolved.

Cannon, again in Kingsley's body, goes to Sovac's home to retrieve the money and intends to murder Jean. The plan underscores how far the Cannon persona will go to secure the fortune. Jean becomes a direct target of the killer.

Sovac shoots the Cannon manifestation, killing him. The immediate threat from the killer in Kingsley's body ends, though the consequences of the experiment linger. Kingsley is left to confront what has happened to him and his identity.

Sovac is executed by electric chair for murdering Kingsley. Before his death, he provides notes on his brain transplant procedure to a reporter, hoping the work might one day be used for better purposes. The ending emphasizes the potential, and perils, of future scientific advancement.