 June 2007 saw the publication of "The Black Diamond Detective Agency", Campbell's adaptation of an as-yet unmade screenplay by C. Gaby Mitchell.Set in the closing months of 1899, it features the eponymous private detective agency investigating a conspiracy to blow up a train, and their prime suspect's efforts to find the truth.In January 2008, First Second Books published Campbell's collaboration with Dan Best, "The Amazing Remarkable Monsieur Leotard".