Abbott and Costello Meet Dr. Jekyll and Mr. Hyde

Slim and Tabby are American police officers sent to London on an exchange to improve their skills.

In Hyde Park, there is an argument between Bruce Adams and his colleague Vicki Edwards. The showdown ends at the police station, but Vicki's guardian-Dr. Henry Jekyll-pulls them out. Dr. Jekyll himself conducts experiments in his home laboratory: after taking a special drug, he turns into his evil alter ego-Mr. Hyde. Jekyll's thoughts about the murder of Bruce when he sees that he likes the Wiki.

Slim and Tabby suspect the doctor of dangerous experiments, and Tabby even manages to catch him red-handed in the wax museum, but he manages to regain his human form before the witnesses arrive. After that, Jekyll invites his American friends to his house, where he treats Tabby with a tincture, and he temporarily turns into a giant mouse. Slim and Tabby try to inform Scotland Yard about the dangerous scientist, but no one believes them.

Vicki informs Dr. Jekyll of her intention to marry Bruce, and Mr. Hyde immediately tries to kill her. The girl is saved by the groom, but the monster escapes. Tabby accidentally injects himself with the doctor's serum and becomes a monster like Mr. Hyde himself. Bruce goes after Mr. Hyde, and Slim goes after Tabby, and everyone is sure that they are chasing the real and only monster. Bruce's chase ends at Jekyll's house, where Hyde falls out of a window and falls to his death, after which a reverse transformation takes place and everyone sees his true identity. Slim grabs Tabby the monster and takes him to the police station, where he manages to bite several police officers before returning to his human form. They turn into monsters and chase Slim and Tabby-man.