Note that these are the traditional fiction versions of these characters I'm suggesting.
In late 19th Century London, the 'Napoleon of Crime' Professor James Moriarty finds his position threatened by two emerging rivals, the Devil Doctor of Limehouse and his associates, and the worrying reports of Romanian Count Vlad Dracula, who has also positioned himself in London with the aim to use it as a vampric power base. Moriarity and Manchu's goals are both threatened by this, but each opposes the other too much to join forces. A power play for dominance on the British Capital commences, with Moriarty having access to Colonel Sebastian Moran and an army of criminal enterprisers, as well as his incredible genius and planning. The Devil Doctor has his own criminal empire based in Limehouse and his powerful Si-Fan forces, as well as his elaborate animal and poison based traps. Dracula has managed to bring with him a small group of his Wrenches via the Dexter and also has those under his thrall in London, and has the natural strengths and weaknesses of a Traditional Vampire. Moriarty and Manchu have no means of determining at this time where Vlad is based so as to assault him in his day slumbers, but both has the means to construct anti-vampire materials as needed. Each of them wish to come to dominate 19th Century London in order to gain a foothold within the wider British Empire.
Who will emerge as the dominant party over London? What might also happen if Sherlock Holmes, Doctor John Watson, Professor Van Helsing, Jonathan Harker, Nayland Smith and a crack squad of Police led by Inspector Lastrade come in a a fourth force to battle the other three groups?