The Perfect Poison by Amanda Quick is the sixth book in the Arcane Society series, and takes place in late Victorian London. This is also my favorite book in the series that takes place during this era.
Caleb Jones has the rare psychic ability to piece together puzzles and solve mysteries and conspiracies. He has founded a psychical investigation society which is primarily concerned with unearthing and destroying a cabal bent on acquiring psychic power. When Lucinda hires him, he begins to realize that there is a connection between the cabal and the theft of her plant. He is also attracted to her, and comfortable with her in a way that he rarely is with people. Slowly they begin to piece together the links between the theft and the cabal, and discover that they make excellent partners in more ways than one.
Lucinda and Caleb are unique individuals that struggle to fit into society. Both powerful psychics and passionate about their vocations, they immerse themselves in their work until they meet one another. Once this happens, they have to reconcile their careers and tendency to go it alone with their new romance. Their relationship and partnership is witty, engaging, and fun to read.