Death Can Be Habit-Forming. John Pickett Mysteries

Having resigned his position at Bow Street in disgrace (at least in his own mind) and failed in his attempt to establish himself as a private agent, John Pickett toils away at a tedious job as a clerk in the City. When he is approached by a man wishing to hire him to extract a young lady being held against her will at an asylum for opium-eaters, Pickett jumps at the chance to prove himself, and has a very reluctant Julia commit him to the institution as a patient.
But nothing at the Larches is exactly as it seems, and while getting in may be easy, getting out may be another matter entirely.