I would also recommend Cthulhu by Gaslight. The low-level grittiness of BRP fits nicely with the theme. If you combine Cthulhu by Gaslight with After the Vampire Wars (for Mythras/BRP) you probably get pretty close.
There’s also ’Hudson & Brand, Inquiry Agents of the Obscure’, published as a supplement for Call of Cthulhu. I have heard good things about it and Stygian Fox usually makes excellent books.
There’s also ’Hudson & Brand, Inquiry Agents of the Obscure’, published as a supplement for Call of Cthulhu. I have heard good things about it and Stygian Fox usually makes excellent books.