The word 'special' in the title refers to a special train - a privately hired train. This is a train a railway company inserts into its regular schedule when somebody pays for the expenses of the locomotive, wagons, and staff to operate the train. It is essentially the equivalent of chartering an airplane at a time when there were no airplanes.
This impossible crime story concerns the baffling disappearance of a special from the London and West Coast Railway Company on its journey from Liverpool to London on 3rd June 1890. Besides the train crew of driver, fireman, and train guard the only passengers are two South Americans. The train is confirmed to have passed Kenyon Junction but never reached Barton Moss. An inspection of the tracks between these two stations did not provide any traces of an accident, derailment, or other clues as to what happened to the train or its passengers. It seemingly vanished into thin air.
This is not a Sherlock Holmes story even though a minor character is implied to be Holmes, though his name is not used and this character does not provide the mystery's solution.
1st edition 1898 in The Strand Magazine; PDF 16 pages.
word count: 7059 which is equivalent to 28 standard pages of text