But Warne didn't leave, and after pointing out to the advantages a female detective would have in certain situations over men, Pinkerton hired her the next day.
Warne became one of Pinkerton's best operatives. The night the Pinkertons protected Abraham Lincoln on his trip through Baltimore for his first inauguration, it was Warne who arranged the railcars, coordinated transportation, and provided disguises. In 1860, Pinkerton had hired several more female detectives and called them his "Female Detective Bureau."
Warne's career, unfortunately, was cut short by illness. She passed away suddenly in January, 1868, at age 35 with Pinkerton at her bedside. She's buried in the Pinkerton Family Plot in Graceland Cemetery in Chicago, IL.
Upon her death, Pinkerton said "She succeeded far beyond my utmost expectations. Mrs. Warne never let me down!"