"The Vanishing Dr. Vespasian" is the first segment of the fourth episode of the third season of Spider-Man. It is inspired by the 1897 novel The Invisible Man and its previous adaptations to other media. It originally aired on ABC on April 12, 1970.
The segment opens with a scientist testing a new experiment. He calls his dog, Brutus, over to drink it after mixing it with milk to make it passable. Eventually, once the dog drinks the whole concoction, it vanishes. The scientist was seeking the power of invisibility, and he found it, after years of other work, including a laser that can melt steel vaults and a magnet that attracts money. The scientist is known as Dr. Vespasian, and he plans to use his discovery for evil, after demonstrating it to some crooks. Meanwhile, Spider-Man is called in by the mayor, and told about a series of bank robberies.
Turns out, the description of the robberies match the previously seen creations of Dr. Vespasian. Meanwhile, the mad doctor demonstrates the results of his creation to the crooks who arrived, and they're all amazed, and their amazement soon turns to terror when the doctor orders his invisible dog to attack. Dr. Vespasian explains that their ultimate goal is the destruction of Spider-Man. Meanwhile, Spider-Man is swinging through the city, when he suddenly sees a bank that was broken into. Spidey goes down to investigate, and when he sees a pair of gloves carrying a box all by themselves, he's caught both in the trap and by surprise when Brutus is ordered to attack. Soon, after a tussle with the dog, Spider-Man gets it covered in flour and traps him, now that he became visible.
The next day, Dr. Vespasian is watching a news report about his exploit, and gets word about special crown jewels arriving in the city. Later that night, Spider-Man has a plan set up for the crooks, and it involves an ice cream machine. Soon, Dr. Vespasian manages to get himself into the vault where the jewels are being kept. Once he pulls out the droor where the jewels are being held, Spider-Man shows up and the trap is sprung. Soon, Dr. Vespasian is covered from head to toe in ice cream, complete with sprinkles. And the episode ends with Dr. Vespasian getting hauled off to the police station in an ice cream truck.