In Season 3, Eliza finds herself investigating more fresh and surprising mysteries, ranging from a disappearing magician to police corruption, as she struggles to build her detective agency. Growing competition from a rival agency creates new problems, and all the while she is still juggling her relationship with Inspector William Wellington, the Duke.

Eliza bumps into Arabella Herbert, the girl who made her life a misery growing up. But as an adult, Arabella seems kind and considerate and everybody loves her. So when Eliza suspects she may be a criminal, no one wants to hear it, least of all Duke.