Millionaire sportsman Grayson Carter is found strangled to death
at the Drexel Club in New York City, and becomes the fifth victim
of the mysterious vigilante known as "Dr. Rx," a physician who
kills crooks who have been acquitted of murder through various
legal maneuvers. The next day, when famed private detective Jerry
Church returns to the city after a year in South America, worried
police captain Bill Hurd tells him that gangster boss Anthony
Zarini has been charged with murder and is being defended by ace
lawyer Dudley Crispin.
When Hurd suggests that he investigate the
case, Jerry tells the captain that he has quit detective work to
return to his family's bond business in Boston. Later, John
Crispin, Dudley's brother, attempts to hire Jerry for his sibling,
and though the detective refuses the job, he agrees to see Dudley
that night at his home on Long Island. Anxious to protect his
client from retribution, Dudley offers Jerry $10,000 to take the
case, with a $10,000 bonus if he finds Dr. Rx. The detective
refuses once again, but reconsiders the offer after a female
prowler is chased off the property.
After leaving the Crispin
estate, Jerry finds a note in his car, advising him to see Barney
Scott in Syracuse. Immediately upon his acquittal, Zarini becomes
the sixth victim of Dr. Rx. Jerry thinks that Ernie Paul, Zarini's
partner, might have killed the gangster, knowing that the mad
doctor would be blamed. Paul, however, has already left town,
having been tipped off by "a woman's voice."
Jerry then finds a
microphone hidden in his apartment. With the help of his butler,
Horatio Pitts Washington, Jerry follows the microphone's cable to
the apartment below, which turns out to be the new home of his
ex-girl friend, mystery writer Kit Logan (Anne Gwynne). After sending Hurd off
on a false lead, Jerry and Kit sneak off to get married. Kit then
goes to Syracuse to see Barney Scott. Scott's mother warns Kit
that her son, once a healthy policeman, was turned into a
white-haired invalid while working on the Dr. Rx case.
day, Jerry is abducted by Paul, who demands that he stay on the
case in order to clear the gangster's name. Back at their
apartment, Kit refuses to believe Jerry's kidnapping story and
leaves him. When Jerry sends Horatio after her, the butler is
abducted by Dr. Rx, who forces him to set up a meeting with his
unsuspecting employer. Kit, Hurd and police sergeant Sweeney
attempt to follow Jerry to the meeting, but the police sergeant
rolls their car while making a fast turn. Back at his hideout, Dr.
Rx makes plans to exchange Jerry's brain with that of an ape.
the Mayview hospital, meanwhile, Kit recovers from her automobile
accident injuries, only to learn that Jerry and Horatio have been
found. Like Scott, Jerry has become white-haired and is almost
comatose. A doctor is brought in to examine Jerry, and when Dudley
offers him his fountain pen, the disguised Jerry jumps from the
bed and arrests the lawyer.
Afterward, Jerry tells Hurd and
Sweeney that Dudley, the real Dr. Rx, had used his fountain pen,
which he filled with a poison that created the appearence of
strangulation, to kill his victims. Jerry saw Dudley's pen while
he was Dr. Rx's prisoner, and further explains that he had not
escaped, but had been let go, as had Scott before him. Jerry and
Kit make up, and all returns to normal, except Horatio's hair,
which has truly turned white.