The Ghost Division by Alydia Rackham

Agent Artful Doyle, the Bureau's expert on Reports and Regulations, has been unexpectedly given an assignment after three years doing desk work. She's been sent to "bring to heel" their foremost Ripperologist, Agent Darrish Fox, who shows signs of going rogue. But when she finally arrives in Victorian London and discovers what Agent Fox has been investigating, she realizes that situations in the field are rarely as cut-and-dried as they are on paper. The Bureau has always used technology that simulates ghosts and haunted houses to disguise their presence in the past, but now, it seems that not all Bureau ghosts are accounted for--and a mysterious entity may be using that same technology for illegal and sinister purposes...