American detectives Slim and Tubby encounter Dr. Jekyll during an assignment in London to compare investigative techniques with their British counterparts. Meanwhile, Dr. Jekyll injects himself with a serum, transforming into the brutal Mr. Hyde, who embarks on a killing spree. As Slim and Tubby aid in the investigation, chaos ensues when Tubby gets injected, leading to hilarious consequences. © 1953 Universal Studios. All Rights Reserved.