The Great Mouse Detective

Set in 1897 London, The Great Mouse Detective opens on young Olivia Flaversham's birthday. Her father Hiram, a gifted toymaker, is violently abducted by Fidget, a bat with a crippled wing and a peg leg who works as henchman for the notorious criminal Professor Ratigan. Alone and frightened, Olivia sets out to find Basil of Baker Street—the rodent world's answer to Sherlock Holmes—but gets lost along the way. She is found by Dr. David Q. Dawson, a kindly army surgeon recently returned from service with the Mouse Queen's 66th Regiment in Afghanistan. Dawson escorts her to Basil's Baker Street residence.

Basil is initially indifferent to Olivia's plight, but the moment she describes Fidget, he snaps to attention: Fidget is the known henchman of Professor Ratigan, a criminal mastermind Basil has obsessively pursued for years. Basil deduces that Ratigan has forced Hiram to build a clockwork robot replica of the Mouse Queen. Hiram initially refuses, but Ratigan threatens to harm Olivia if he does not comply, so Hiram relents. Ratigan's plan is to use the robot queen to seize the throne and declare himself Supreme Ruler of all Mousedom.

Basil, Dawson, and Olivia borrow Toby—Sherlock Holmes's pet Basset Hound, who lives in the human world above—to track Fidget's scent. The trail leads them to a toy shop where they find Fidget stealing clockwork components and toy soldiers' uniforms needed to outfit Ratigan's mechanical minions. During the confrontation, Fidget ambushes and captures Olivia. Basil and Dawson pursue but are outmaneuvered and lose the trail.

Basil pivots, disguising himself and Dawson as sailors. They infiltrate a seedy waterfront tavern called the Rat Trap, where they spot Fidget. They follow him back to Ratigan's cavernous underground headquarters, only to walk into an ambush. Ratigan, reveling in his apparent victory, has both Basil and Dawson bound to an elaborate Rube Goldberg killing machine—a spring-loaded mousetrap connected to guns, a crossbow, an anvil, and a phonograph—set to trigger in sequence and guarantee their deaths. Ratigan then departs for Buckingham Palace, where his henchmen, disguised as royal guards, have kidnapped the real Mouse Queen.

At the palace, Ratigan presents the clockwork queen to an assembled royal audience. The robot regally announces Ratigan as supreme ruler and condemns all who oppose him. Just as the coup appears complete, Basil and Dawson arrive—having ingeniously reverse-engineered the timing of the death machine to escape it. They expose the robot for what it is, rescue the real Queen, and free Hiram Flaversham. Ratigan's scheme collapses.

Ratigan grabs Olivia and escapes aboard his personal dirigible. Basil and Dawson give chase, ultimately catching up with the craft. The climactic confrontation plays out high inside the gears and bells of Big Ben. As the clock strikes ten, the massive gear-works shake and destabilize the fight. Ratigan, stripped of his cultured veneer, reverts to feral savagery and nearly kills Basil—but the violent tremors of the striking bells send Ratigan plunging from the clock tower to his death far below. Basil, barely surviving, catches a piece of the destroyed dirigible and glides safely down to rejoin Dawson and Olivia.

The film closes back at Baker Street. Olivia is reunited with her father; a new client appears at the door almost immediately. Dawson, who initially planned only to escort Olivia, decides to stay on as Basil's full-time partner and companion.

Sources: Wikipedia, OMDb, Web search (Disney Wiki / Fandom search snippets)