"Sherlock Holmes in the 23rd Century" is the title of two 1988 episodes from the Filmation cartoon series BraveStarr. They're on Hulu, but are incorrectly titled as the "21st century", contradicting the credits and dialogue in the actual videos.
If you don't know it, BraveStarr is a space western set in the future on the planet New Texas, where Marshall BraveStarr and his friends battle outlaws who are after the valuable mineral Kerium. BraveStarr also has supernatural powers based on "spirit animals"--puma, bear, wolf, and hawk. I don't remember most of the show, but am sure it was in my rotation of cartoons in my childhood.
The first Holmes episode begins on Earth in 1893 at Reichenbach Falls; clearly they have mistaken Final Problem's publication date for the date the story was set, in 1891. During a torrential thunderstorm, Holmes battles a ghoulish Moriarty, and Watson stands on a ledge below them, shouting for Holmes to move back from the cliff so that Watson can shoot Moriarty. Holmes falls over while weird lightning strikes and a vortex forms into which he disappears. A strange newspaper comes out of the vortex and gets blown to Moriarty, who catches and reads it with interest. Meanwhile, Watson shoots at Moriarty but misses, and Moriarty turns away. We don't see exactly how he disappears, and instead see the rain stop as Watson mourns Holmes and says farewell.
Cut to the year 2249 on Earth, apparently in London, given the view of Big Ben. Even though the clock face has been changed to digital, and some buildings look art deco, the city resembles a steampunky Victorian London. (A news reporter later calls the area Old New London!) The people all dress and talk like Victorians, even Dr. Whitson, who is a green-skinned alien with a white mustache. With lightning bolts, Holmes suddenly falls out of the sky and crashes into a hansom cab (not horse-powered, at least). Whitson gets in and orders the cab to Harley Street Hospital, where he fixes Holmes's many broken bones with some kind of machine. As Holmes lies on the table, he wakes and sees all the strange lights and machinery above him, so he asks where and when he is. Whitson tells him the year, and Holmes notices that the doctor is not human. Whitson says he's Rigellian, and Holmes deduces what the planet is like based on Whitson's appearance. He doesn't seem fazed by waking up in the future at all. Holmes is sitting up, his nakedness only covered by the sheet, and he looks muscular and square-jawed like an action hero such as He-Man (or BraveStarr himself) rather than the thin man in Paget's drawings. He soon tells Whitson who he is, but in a strangely sinister way. Hey, maybe he's having belated shock about waking up in the future after all?
Meanwhile, out on a Old New London street, Marshall BraveStarr is watching a news report about space pirates hijacking a freighter ship from New Texas, carrying Kerium ore. Then the reporter mentions Sherlock Holmes appearing, apparently due to a rare "natural time warp," and she says that Holmes plans to visit the current 221B Baker Street and meet Mycroft Holmes, who is a direct descendent of the original Mycroft.
Holmes and Whitson stand outside observing street life when Holmes discovers that he can produce electricity from his fingers. He likes this side affect of his trip through the time warp. They then meet some pickpocket urchins with a dog named Baskerville, but are soon attacked by a bunch of robots. The kids get away, and Holmes starts shooting electricity to defend himself and Whitson, but they are still outnumbered. Mycroft comes to their aid, and she turns out to be a blonde woman with a big hulking laser gun. She's apparently some special agent at Scotland Yard, and she calls Chief Inspector Kitty Lestrade to have the robotic goons taken to jail. For simplicity's sake, she calls Holmes, "uncle Sherlock", and they head to 221B Baker Street, which is of course, a museum. I'm glad that Holmes at least said sadly, "everything's here but Watson."
There's a knock at the door, and Marshall BraveStarr arrives with a case for Holmes. BraveStarr explains that the reason he left New Texas is that he's looking for a mysterious alien boy that stowed away on the freighter ship that was hijacked. All the passengers were released and accounted for except the boy, Fleeder, and BraveStarr feels responsible for the runaway. Earth is also way out of his jurisdiction, so he'd like some help finding Fleeder. Mycroft and Whitson both offer to help as well.
Suddenly a fog creature appears in the room and kidnaps Holmes. Everyone gives chase, but BraveStarr's attempt to use his "speed of the puma" is thwarted by Mycroft accidentally shooting him. Meanwhile, the pickpocket boys save Holmes from Fog (who materializes as a stereotypical Scottish character), and the others catch up after the boys leave. Back at Baker Street, they contain Fog in a glass object, and Chief Inspector Kitty Lestrade arrives to help question Fog. She is a redhead and seemingly flirts with Holmes for just a moment before bantering about how Mycroft is violent but effective. Eventually Fog confesses that he was hired to kidnap Holmes by some anonymous guy paying with Kerium ore. Holmes points out the connection to the freighter, and everyone but Lestrade leaves to check out the warehouse that Fog was supposed to take Holmes to. When they arrive, they obviously fall into a trap, and thus ends part 1.
In part 2, the news reporter summarizes part 1, and we rejoin Holmes, Whitson, Mycroft, and BraveStarr in an underground pit. The marshall hears Fleeder singing, so they rush to find the boy alone in a cell. His singing is hypnotic, making them see visions of outer space; clearly he is magical. As they explore around the underground lair (which is actually pretty huge and even has an overgrown greenhouse that somehow survived without sunlight), they find the hijacked freighter ship and other clues. Holmes soon deduces that Moriarty is behind all this, but Moriarty arrives then with a bunch more goons. Mycroft and BraveStarr are quickly knocked out and captured, while Moriarty evilly gloats at Holmes. He explains that after he caught the newspaper from the future and read about Holmes reappearing, he built a suspended animation chamber so that he could sleep for 350 years and defeat Holmes again. However, he also hijacked the freighter for money to fund his plans, and he discovered the magical Fleeder onboard; now he plans to conquer the world using the boy's powers. Apparently not caring about killing Holmes himself anymore, Moriarty leaves with his hostages, but orders a few goons to stay and kill Holmes and Whitson (or maybe not kill, because all these cartoons back then avoided deaths whenever possible). This time Holmes fights off all the goons with his electricity, and Whitson is strong enough to tie them up with metal bars. Holmes then picks up a fragment of Moriarty's cape and decides to follow his trail with help from the urchins' dog Baskerville.
They lose the trail at a "turbo station" connecting Old New London with Paris, and they hire a dirigible to take them to Paris. Holmes explains that he's figured out Moriarty's plan to conquer the world. Some of Moriarty's henchmen are members of the "hypno-rock" band Discord. Hypno-rock is illegal because the music is altered to hypnotize people and make them do weird things. If Moriarty can use Fleeder's hypnotic songs in the same way, then he can control the world. All he needs is enough amplification and a powerful antenna. Hence his trip to Paris, to use the Eiffel Tower. (Moriarty had purchased it with his Kerium ore, and now it's rigged up with all the equipment he needs to broadcast worldwide.)
So on the tower, Moriarty gives Fleeder the mind-controlling lyrics he wants the boy to sing, but Fleeder refuses. Moriarty threatens Mycroft and BraveStarr, who are tied up and hanging precariously from a crane. Fleeder reluctantly sings his song for Moriarty's broadcast, and the world is enslaved, except for Holmes's crew apparently. They interrupt the broadcast and free the hostages, who join Whitson and the urchins on the dirigible. Mycroft wants to go in guns ablazing after Moriarty, but Whitson explains that Holmes has a different plan. Holmes tells Fleeder to sing a song to his parents so they can hear him. Fleeder then sings a song of love, and the world is free. Moriarty tries to kill Holmes, who is weakened, but then Fleeder's lost parents arrive. They are magical beings who look like giant, silhouetted fairies, and they are grateful to find their lost son. They restore Holmes's health and then fly to another galaxy with Fleeder.
Moriarty is defeated, and though it almost looked like he died, he is actually hanging off the Eiffel Tower by his cape. Mycroft will call Lestrade to pick him up. Holmes joins the others on the dirigible, and they discuss the magical Fleeder. BraveStarr thanks Holmes for his help, then says he better head back home to New Texas. Holmes says goodbye and says that he hopes to have more exciting adventures with Whitson, Mycroft, and even the boys, so long as they give up stealing. So ends another 1980s cartoon with a moral lesson.
Thus Holmes stays in the 23rd Century, never returning to the past, unless some other freak time warp aims him back at the 19th century. Poor Watson, left behind and replaced, just like in Sherlock Holmes in the 22nd Century. (Or maybe a replacement Holmes did come to Watson, as some Sherlockians suggest that the post-Return Holmes was a little too different?) Just as long as Watson's happy, I say.
It's weird how in part 2, BraveStarr and Mycroft were out of commission so that the story could focus on just Holmes, Whitson, and the boys for a while. BraveStarr is like a guest star in their world instead of vice versa. It almost felt like a backdoor pilot for a TV show that never got made. (I wonder if the later 22nd Century series was inspired by this BraveStarr story. Not that the stories and characters were the same, but just the general concept of Holmes in the far future, solving new mysteries.) It's also quaintly laughable now to think that newspapers were assumed to still be around in the 23rd Century, given the dying newspaper industry now. But maybe the print news eventually came back into fashion along with all the retro clothes and mannerisms? Who knows?