The year is 1897. The place is London. The setting is not our world, but the world of England's mouse population, who live lives not so different from ours, in the mouse holes and basements of the British Empire.Hiram Flaversham, a master toymaker, is kidnapped on his daughter Olivia's birthday. The young girl has no one to turn to for help, so she strikes out on her own, seeking the greatest detective in all mousedom, Basil of Baker Street.En route, Olivia encounters Dr. David Q. Dawson, a mouse recently returned from military duty in Afghanistan. The kindly doctor agrees to accompany the girl in search of Basil.They manage to find his rooms at 221 1/2 Baker Street (in the basement of a very famous address), and the mouse himself soon makes his appearance. Basil is a bundle of energy, running around the flat, ignoring his two visitors, in anticipation of bringing his latest case to a successful conclusion with an experiment in ballistics. Alas, the experiment is a failure, and the detective is thrown into a deep depression, still unwilling to help poor Olivia.When the girl mentions that her father was kidnapped by a peg-legged bat, however, Basil is again galvanized into action. This bat, Fidget, is a thug employed by his arch-nemesis, Professor Ratigan!Ratigan is the worst criminal in London, a veritable Napoleon of Crime. Even as Basil recounts his previous battles with Ratigan, the crimelord is deep in the sewers of London, forcing his victim Flaversham to build some diabolical device. What is Ratigan planning? Nothing less than the demise of the Queen on the day of her Diamond Jubilee and his own ascension to the throne!Ratigan's henchmen sing his praises, but their boss shows his true colors when one besotted mouse forgets himself and sings out, "Ratigan, the world's greatest rat." Outraged at being called a rat, although he clearly is one, the professor summons his own personal enforcer: an obese cat named Felicia, who keeps the minions in line and eats those who run afoul of Ratigan's temper.Back in Baker Street, Basil agrees to take the case, and attempts to deduce Ratigan's motive in kidnapping a toymaker, when his cogitations are interrupted by the selfsame Fidget spying in the window!Instantly, Basil is after the villain, with Dawson reluctantly in tow, but all they find are peg-legged footprints and the bat's cap. For a detective of Basil's caliber, these clues are more than enough, and he is off to find the kidnapped Flaversham. Basil wheedles Dr. Dawson into enlisting as his assistant, and little Olivia tags along, too, much to Basil's disgust.The threesome make their way to the human residence above, where they find Toby, a huge hound...well, huge in comparison to a bunch of mice. Toby's keen nose picks up the scent from the dropped cap, and he is swiftly on the trail, a trail that leads to a human's toy shop. Basil skulks about in search of Fidget and finds some puzzling clues: toy soldiers without their uniforms and wind-up toys with all the gears missing.While the detective ponders these clues, Fidget strikes! He stuffs Olivia into a sack and attacks Basil and Dawson with a succession of giant toys, finally escaping through the skylight a hairsbreadth ahead of Basil.Fortunately, Fidget has dropped another clue in the form of a list given to him by Ratigan. Basil's knowledge of chemistry enables him to analyze the paper, finding traces of brandy, coal and seawater, which lead him to deduce that the note came from a seedy pub located where the sewer connects to the riverfront.Basil is also a master of disguise, and he swiftly outfits himself and the protesting doctor as sailors. Together they infiltrate the Rat Trap, a disreputable pub filled with low-life ruffians, just the place to search for one of Ratigan's minions.They do find Fidget, and follow him through the sewer to Ratigan's secret lair, where they spy Olivia held captive inside a huge bottle. While attempting to free her, however, Basil and Dawson are surprised by Professor Ratigan's entire gang, who were just waiting for him to arrive. It's a trap, and Basil fell for it!Delighted at having his greatest enemy in his clutches, the flamboyant Ratigan must destroy the detective in some spectacular way. So, he has Basil and Dawson tied to a mousetrap which will snap when a metal ball drops onto the trigger. Not content with this, Ratigan has set the snap of the mousetrap to fire a gun and a crossbow at the unlucky pair, which will in turn cause an axe to chop them to bits, which will bring an anvil down on whatever is left of the great mouse detective. The entire trap is set in motion when a record of Ratigan's song plays to the end, pulling a string that releases the fatal ball.Alas, Ratigan must away to Buckingham Palace, taking his prisoners and his gang with him, so he provides a camera to automatically record the death of Basil for posterity.Mortified at being outwitted, Basil is once more plunged into depression and puts up no resistance, not so much as attempting to think of a way out of the trap. Only Dawson's determined persuasion snaps his companion out of it, just in time to work out a complicated but ingenious solution. Their only chance is for Basil and Dawson to snap the mousetrap themselves at just the right moment. The trap clamps down on the metal ball, thus protecting the pair from being caught in its powerful jaws. Moreover, the pressure pops off the mousetrap's hinge, which knocks the gun aside, which shoots the crossbow, which deflects the arrow, which shoots the axe, which comes down between Basil and Dawson, which cuts them free just in time to avoid being splatted by the anvil. Whew!Basil is himself again, ready to tackle Ratigan once more, but first not forgetting to pose for the professor's camera. Toby carries Basil, Dawson and Olivia to the palace, where Ratigan's lackeys, dressed in uniforms stolen from the soldier dolls at the toy shop, have already captured the mouse queen. Basil arrives in the nick of time and pulls Her Majesty from Felicia's waiting jaws.Meanwhile, Ratigan has substituted a mechanical queen for the real sovereign, a machine built by master toymaker Flaversham. This clock-work queen appoints none other than Professor Ratigan as her royal consort, giving the fiend control over the entire British Empire! But Basil soon intervenes, capturing Ratigan's henchmen and exposing the villain for what he truly is: a slimy, contemptible sewer rat!The jig is up, and Ratigan flees with the faithful Fidget and with Olivia as his hostage in his monogrammed, bicycle-powered dirigible. Toby makes short work of Felicia as Basil rigs up a pursuit vehicle out of a Union Jack, a matchbox and a bunch of balloons. He chases Ratigan across the London skies, and the fiendish professor attempts to lighten his own load by tossing Fidget overboard! But he can't escape Basil, who fearlessly leaps onto the dirigible. Suddenly, the Houses of Parliament loom ahead. Basil and his enemy crash into the face of the famous London landmark, the clock commonly known as Big Ben.Inside the tower, Basil and Ratigan battle on the huge mechanism, where any false step could crush them between the meshing gears. Ratigan is much bigger and more powerful, and Basil just manages to scoop up Olivia and head for safety atop the tower. But Ratigan's rage at being thwarted once again causes him to snap. He rips his clothes to shreds and stands revealed as a fierce and deadly rat!Olivia is safely aboard the balloon, but Ratigan tackles Basil and the two go tumbling down to land on the hands of the great clock. The detective is battered mercilessly until he finds himself hanging by his fingernails on the edge of oblivion. The evil Professor Ratigan has won, but wait! He hasn't been paying attention to the time. But Basil has, and he watches with satisfaction as the vibrations from the chiming of the bell when the clock strikes the hour send Ratigan over the edge. At the last moment, the villain manages to pull Basil down with him.Anxiously, Basil's friends watch both detective and crimelord plunge into the fog to the river far below. It looks hopeless, but the remarkable Basil is able to use the propeller from the dirigible to save himself, creating a pedal-powered helicopter that lifts him to safety.The empire is saved, Olivia is reunited with her father, and Basil invites Dr. Dawson to be his partner in crime-detection. As a tearful new client appears at 221 1/2 Baker Street, bringing a new case with new adventures, we take our leave of Basil of Baker Street, the Great Mouse Detective.
Output: Question: What river did the checklist come from?, Answer: A sewer that connects to the river.