But one of Garth's patients dies during a test of the serum, and the doctor is found guilty of murder and sentenced to hang. In prison, a lenient warden allows Garth to continue his peculiar brand of medical research.

Assisted by colleague Dr. Howard (Van Sloan), Garth completes the formula for his 'anti-death' serum - by using the blood of a fellow inmate...a convicted serial killer. He tests the serum on himself, and quickly discovers it's taken 20 years of age away.

Yet, something isn't quite right. Garth is secretly overtaken by fits of uncontrollable rage and violent urges to kill! Nevertheless, he's pardoned for his scientific rewards and re-enters public life...only to find he's become a psychotic maniac!

This rather routine 1940 Columbia horror is enlivened by a classy performance from Karloff and enhanced by thematic echoes from 1931's Frankenstein. Boris is poignant and sympathetic as the beleaguered Garth, and his assault on Van Sloan ranks as one of the best scenes of this minor terror outing.