Allan J Pinkerton, a Scottish cooper or maker of wooden casks and barrels and an abolitionist, immigrated to America in 1842 and initially set up a shop as a cooper in Dundee, Illinois. He first became interested in criminal detective work, when one day while wandering through the wooded groves around Dundee, looking for trees to make barrel casks, he came across a band of counterfeiters. After carefully observing their movements for some time, he informed the local sheriff, who arrested them. The incident led to his appointment as the first police detective in Chicago, Cook County, Illinois, in 1950.

Subsequently, after serving as a deputy sheriff in two Chicago-area counties, he became a special agent for the US Post Office in Chicago and after that, started his own private detective agency, named Pinkerton Detective Agency, the first of its kind in the country. The group successfully handled a wide range of cases, from white-collar crime to thefts to cons as well. However, the agency achieved a little bit of national recognition before the Civil War.

On a hot summer day in 1856, Kate Warne, a 23-year-old woman, walked into the office of Pinkerton Detective Agency and met detective Allan Pinkerton in response to an advertisement for the recruitment of detectives he had placed in a Chicago newspaper. Pinkerton thought that the slender young woman standing in front of him with eyes filled with fire and graceful in her movement had misunderstood the advertisement and was looking for a clerical job. He, therefore, immediately made it clear to her that he was not looking for a secretary.

However, he was surprised to learn Kate was not looking for clerical work, but was actually answering an advertisement for detectives he had placed. When Pinkerton wanted to make her understand by saying that it is not the custom to employ women detectives, Kate argued that women could be a key component when it came to gathering intelligence, as women have an eye for detail and are excellent observers. She specifically pointed out that women could be most useful in worming out secrets in many places which would be impossible for a male detective, as a woman is better placed than a man to befriend the wives and girlfriends of suspected criminals and gain their confidence. In addition, she would also be able to take advantage of the fact that men tended to brag when women were around. Her arguments worked and Kate Warne walked out of the office with a job as a detective. Within a few years of her joining the Agency, Pinkerton named her one of his five best detectives and began a Female Detective Bureau headed by Warne. However, despite the success of Warne and other women working for the Pinkerton Agency, America would not see its first female police officer until 1910.

Very little is known about the early life of Kate Warne, except that she was born in 1833 in Erin, Chemung County, New York and was already a widow at the age of 23, when she joined the Pinkerton. She never remarried, but it is widely believed that she had a long affair with her married boss, Allan Pinkerton, and they often played the role of husband and wife while on assignment. She used around 12 pseudonyms, every one of them is a very slight variation on her actual name, like Kate, Kay, and Kitty, while her fake last names included Warren, Waren and Warne, her actual last name.

However, she became an expert in hiding her identity in disguises, changed her accent at will and was remarkably successful in her profession as a detective and wartime spy, possibly because no one suspected her as a female detective, rarely known in those days. However, perhaps to protect her identity or a family back home, Kate Warne kept her life a secret and no confirmed photograph of her exists, except just a single watercolour portrait.

In 1858, Kate Warne was entrusted with the task of obtaining a lead on a case involving the theft of $10,000 from the Adams Express Company railroad. A man named Nathan Maroney, the manager of the company’s Montgomery, Alabama offices, was suspected of the theft, as he was believed to be the last employee to see the money before it disappeared. On her arrival in Montgomery, Warne changed her Northern accent with a Southern one, befriended Maroney’s wife and she soon divulged that her husband had taken the cash and hidden it in Jenkintown, Pennsylvania. Finally, Nathan Maroney was convicted, after he confessed his crime and all but a few hundred dollars were recovered.

Like a chameleon, Kate Warne had the ability to adapt, which gave her a huge advantage as a detective and by presenting herself as a fortune teller, she once thwarted a plot to poison a wealthy Captain Sumner. Before proceeding in the matter, she quickly learned about the subject from books in a space rented out by Pinkerton to ply her trade. After that, she hosted Sumner's sister, Annie Thayer, who became very much impressed by Warne’s knowledge of life, which she gathered earlier from the Pinkerton agents. Believing that Warne had a real gift for divination, she eventually divulged that under influence of Mr Pattmore, her lover, she assisted him in the murder of his wife and her own brother, Captain Sumner, so that they could enjoy his fortune. Eventually, the pair were caught before they could murder Sumner and Pattmore, convicted of his wife's murder and had to spend 10 years in prison.

However, the highlight of her life is thwarting the Baltimore Plot, in which Kate Warne saved the life of the President-elect Abraham Lincoln by uncovering the key details about the plot of his assassination. In early 1861, Pinkerton Detective Agency was hired by Samuel Felton, president of the Philadelphia, Wilmington and Baltimore Railroad, to investigate secessionist activity in Maryland. During that time, Felton became concerned about threats of damage to the railroad by the secessionists of Maryland, which perhaps also included an assassination plot of the would-be president of the country. Kate Warne was part of the Pinkerton team sent to Baltimore on 3 February 1861. Using the aliases Mrs Cherry and Mrs M Barley, Warne infiltrated secessionist social gatherings, posing as a flirting Southern belle with a thick Southern accent, in the classy Barnum Hotel. From the gathering she came to know that the hatched plot not only involved the damaging of the railroad, but also included the assassination of the President-elect Lincoln, while he would be changing trains in Baltimore on his way to the capital to take the oath of office. She also came to know that the assassination was to take place at the Calvert Street depot, where a large crowd of secessionists would be assembled to wait for the train carrying Mr Lincoln. They would arrive early to clog the narrow streets in the immediate area, while the Marshal of Police would arrange only a small number of policemen to protect the president-elect. On the arrival of the train, a group of men would engage in a conflict nearby and the police would be dispatched to attend to that skirmish, while Abraham Lincoln would be surrounded by a crowd and would be stabbed by the men in the crowd.

In a specially arranged meeting, Lincoln gave a patient hearing to Allan Pinkerton, interrupted with many questions and then finally agreed to place himself in the protective custody of his agency to get him safely to the capital for his inauguration. Kate Warne, who was a key player to uncover the assassination plot, also carried out most of the arrangements to smuggle Lincoln into Washington. She suggested that rather than ride publicly through the city streets between train stations in Baltimore as planned, the future president should take a midnight train straight through to the capital, without stopping in Baltimore to make a speech. Accordingly, an elaborate plan was hatched by Pinkerton and his detectives to protect Lincoln as he will be travelling 200 miles in a single night to reach Washington, DC. Pinkerton also formulated a scheme which involved bringing Lincoln to Baltimore in advance of his expected arrival and cutting off telegram lines to keep the miscreants in the dark about Lincoln’s whereabouts.

Accordingly, on Feb. 22, while dining at the Jones House, Lincoln feigned exhaustion and retired for the evening to slip out a side door and into a waiting carriage wearing a wool hat and shawl. After that, he boarded a Pennsylvania Railroad train for Philadelphia at 6:00 pm to switch to an 11:00 pm Baltimore-bound train. By that time, Kate Warne had secured four berths on the train to Baltimore as Mrs Cherry for her invalid brother and other family members and bribed a conductor for a special favour of privacy, as she would be travelling with her invalid brother. At the same time, the tracks were instructed to be kept clear so that the train could go full speed all the way. At the station, Warne entered the sleeping car through the rear along with Pinkerton, Ward Hill Lamon, a personal friend and self-appointed bodyguard to Lincoln and a disguised president-elect Abraham Lincoln. The train pulled out around 11 pm and as they travelled through the night, Warne gripped a pistol she carried, while her companions stood to watch at every switch, bridge and crossing, believed to have inspired the Pinkerton Agency’s slogan, We never sleep. The presidential party arrived at Baltimore about 3:30 am on February 23, hours ahead of his anticipated arrival, where an express train, arranged by Warne, was waiting. However, as a special arrangement, instead of being transferred by a carriage, Lincoln’s sleeping car was shifted to another engine, which arrived in DC safely, around 6 am.

With Lincoln in office, Pinkerton went to work for him, together with Warne, throughout the American Civil War, posing undercover as husband and wife to infiltrate shady circles of the criminal underworld. Unfortunately, while she thrived in a dangerous profession, Kate Warne, the first female detective of America, did not live long and passed away from pneumonia in 1868. She was buried in the Pinkerton family plot, ensured by Allan Pinkerton in his will that her plot would never be disturbed.