Mr. Hyde is the criminal alter-ego of physician Dr. Henry Jackal, the head physician at St. Cohen's Hospital, possibly in London.
When his philandering wife neglects him, Dr. Jackal tries to make several attempts to eat at work, but he gets constantly interrupted and distracted by nurses and patients. One elderly patient (Jackie Wright) tries using a leather restraint on his head after his nurse (Alison Bell) mistakes the device he needs for headphones. Another nurse (Samantha Spencer Lane) uses a personal urinal next to a mummified traffic cop (Ken Sedd?) as a vase for flowers. When Dr. Jackal calls upon three attending physicians (Ken Sedd, Bob Todd and Henry McGee) to a consultation, a maintenace man (Jackie Wright) slips in to take a look. Meanwhile, the head nurse (Lee Gibson) keeps snatching up all food he tries to eat. When he finally gets some grapes, the scent of a steaming urinal pan kills his appetite and he passes out.
Desperate to get something to eat, Dr. Jackal retreats to his office and mixes up the chemicals and pills there and is stunned when he transforms into the ruthless but simple-minded Mister Hyde. As Hyde, he's briefly scared of the skeleton display in his office, but he soon launches a spree of public mischief escalating into acts of crime. He tries stealing a child's piggy bank, he buys a snake he takes for a walk at the park, he picks the purse of a lady (Lee Gibson) through the shelves at the library and peeps at a changing young lady (Louise English) before getting grabbed by two off-duty bobbies (Ken Sedd and Henry McGee). When they stop at a tavern on the way to the jail, Hyde's drink restores his metabolism to normal, and he reverts back to Dr. Jackal. Unaware this has happened, the police let Dr. Jackal wander off as they look for Mr. Hyde.
Returning home, Dr. Jackal fails to find any food, but he still has two uncooked eggs leftover from breakfast. Returning to the hospital, the head nurse shows him a patient (Ken Sedd) running a fever, and he uses the fever to cook the eggs on the man's abdomen. Unfortunately, the nurses catches him and takes his fried eggs away. Escaping back to his office, he finds his brew still cooking from before and drinks it, becoming Mr. Hyde again and terrifying an errant nurse (Alison Thomas). He heads to St. Eamons Golf Club and picks the pocket of a golfer (Ken Sedd) hit by a golf ball, also meeting up with two partners (Jackie Wright and Henry McGee) who help him launch a major pick-pocket scam at the park. With this escalating crime spree, the police chief (Bob Todd) calls in Wonder-Gran from the Sunny Days Nudist Camp for help. Posing as a teller, she blasts Mr. Hyde and his gang with a cannon when they came to rob the bank where she is working. She pursues them to St. Eamon's where Hyde and his gang joined by two more rogues (Bob Todd and Ken Sedd) and battle it out in a series of skirmishes and even almost succeed in blowing her up or tossing her in a swimming pool. After she proves impervious to the items they use as weapons, Wonder-Gran gets her foot stomped by one of the criminals (Jackie Wright), departs and returns with a rifle hidden in her crutch. Several lady officers come to round up the gang, but Wonder-Gran takes Mr. Hyde home to reform him. he turns out to be a a bull in a china shop as he distractedly wrecks and destroys her modest home. Once he gets food into his stomach to counteract the potion, he reverts back to kindly and misunderstood Dr. Jackal. The presence of the normal looking doctor suddenly in her home frightens Wonder Gran so badly that she rides away on her jet-powered bicycle.
- Dr. Jackal and Mr. Hyde were both played by Benny Hill.
- This character is a spoof of the titular character from the book, "The Strange Case of Dr. Jekyll and Mister Hyde" by Robert Louis Stevenson.
- The hospital scenes appear to have been filmed in a real hospital, possibly the same one from Lower Tidmarsh Volunteer Hospital; the mansion scenes also appear to be filmed in a real location outside the studio.
- Ken Sedd noticably flinches as Benny breaks the eggs on his head.
- Clare Smalley and Alison Thomas play the nurses in the hallway with Lee Gibson.
- When Dr. Jackal discovers the effects of his formula and looks at his hands, it's very obvious Benny is wearing rubber gloves with fake hair glued to them.
- Wonder-Gran finds the police Captain at the Sunny Days Nudist Colony, roughly the same location as the Rogue Nudist.
- The park-goers are Bob Todd, Louise English, Lee Gibson, Alison Bell, Ken Sedd and Clare Smalley.
- At the park, Henry McGee gets pelted by Alison Bell and Clare Smalley.
- Through the sketch, several locations from other sketches are seen. The bench scene is on the field from the Keep Fit Brigade, the fence along the road is Jed Jardine's country road in Big Poppa and part of the chase scene occurs near the mansion at the start of the Scouts and Guides Annual Fete. Wonder-Gran's cottage stays in the background of nearly all the park scenes.
- Louise English appears at the end playing a little girl who loses her hula hoop to Dr. Jackal.
- This sketch appears on the Video Spotlight VHS Tape from HBO Entertainment.