Abbott and Costello Meet Dr. Jekyll and Mr. Hyde (1953)

A rash of horrific murders has terrorized London and baffled
police. Newspaper reporter Bruce Adams finds one murder victim, a
prominent doctor, while returning home from a pub. The next day,
two American policemen, Slim and Tubby, who are studying London
police methods, respond to brawl at a women's suffrage rally in
Hyde Park. Reporter Adams, young suffragette Vicky Edwards, Slim,
and Tubby are all caught up in the fray and wind up in jail.
Vicky's guardian, Dr. Henry Jekyll, bails Vicky and Adams out,
while Tubby and Slim are kicked off the police force. Unknown to
anyone, however, Dr. Jekyll has developed an injectable serum
which transforms him into Mr. Hyde -- the "monster" responsible
for the recent murders. Dr. Jekyll, who is secretly in love with
Vicky, notices Vicky's and Bruce's mutual attraction. He injects
himself to transform once again into Hyde with the intent of
murdering Adams.


Meanwhile, Tubby and Slim realize that they must capture the
monster in order to be reinstated on the police force. Walking
down a street at night, Tubby spots Hyde (whom Slim at first
mistakes for a burglar) and the boys trail him into a music hall
where Vicky is performing and Adams is visiting. A chase ensues,
and Tubby manages to trap Hyde inside a cell in a wax museum.
However, by the time Tubby brings the police inspector, Adams and
Slim to the scene, the monster has reverted to the respected Dr.
Jekyll, and Tubby is once again rebuked by the police inspector.
The "good" doctor, however, asks Slim and Tubby to escort him to
his home. Once at Jekyll's home, Tubby and Slim snoop around and
Tubby drinks a potion which transforms him into a large mouse.
Slim and Tubby bring this news to the inspector, but the
inspector refuses to believe them.


Later, Vicky announces to Jekyll her intent to marry Adams, but
Jekyll does not share her enthusiasm and transforms into Hyde
right in front of her and attacks her. Adams, Slim and Tubby save
her in the nick of time, but Hyde escapes. During the struggle,
Jekyll's serum needle falls into a couch cushion, which Tubby
accidentally falls onto, transforming him into a Hyde-like
monster. Another madcap chase ensues, this time with Adams
chasing Jekyll's monster and Slim pursuing Tubby's monster, since
both believe they are after Jekyll. The police are frustrated and
confused by reports of the monster seemingly being in multiple
places at once.


Adams' chase ends up back at Jekyll's home, where Hyde falls from
an upstairs window to his death, then transforms to his true
identity. Meanwhile, Slim brings Tubby, who is still in monster
form, to the inspector's office. Tubby bites the inspector and
four officers, then reverts to his true self. Before Slim and
Tubby can be reprimanded, the inspector and the officers
transform into monsters. Slim and Tubby dash through a wall and
out of police headquarters.