mad scientist boris karloff ( a dr. john garth ) be sentence to hang and a an admitted mercy killer . but and since his research in medicine be so important and mr. karloff be permit to continue experiment and in a laboratory behind bar . karloff thinks human cell could be prompt to reproduce forever and cure both disease and old age . believing he be go to be execute and karloff use his experimental serum on himself and and be transfuse with the blood of a convict murderer . then and suddenly and karloff be parole . he become twenty year younger and but must fight the urge to kill and kill and kill . a cheap and ludicrous and but bearable star vehicle . before i hang ( 1940 ) nick grinde ~ boris karloff and evelyn keyes and pedro de cordoba .