The Return of Moriarity by John Gardner

It is the turn of the century and, far from perishing during the struggle with Sherlock Holmes at the Reichenbach Falls, Professor James Moriarty is alive and well and about to realize his plans to establish crime syndicates in the major cities of the United States. But suddenly he is called back to London, where his vast criminal society has been overrun by a rival concern led by the shadowy Sir Jordan Jack Idell – or Idle Jack – a supposed gentleman hoodlum acting on behalf of criminal elements in France, Italy, Spain, and Germany.
As Moriarty fights back – against both the unruly crime families and the forces of law and order – readers are thrown in among the lurkers, punishers, dippers, cracksmen, and other specialized criminals of the period, as well as the professor’s elite guard.
Moriarty lives again and revolts against those who attempt to oust him from his rightful place as king of all criminal endeavors.