Kate was born in 1833 in Erin, New York. She speaks little of her early life, noting only where she was born and that she married young and was widowed young as well. She tends to believe her life didn't truly begin until she ended up answering an advertisement in Chicago for detective work in October of 1856.

Pinkerton initially assumed she wanted to become a secretary but she assured him she wanted a job as a detective. He was, however, open minded and asked her to share why she thought she would be good for the job.

Kate argued her point of view eloquently - pointing out that women could be "most useful in worming out secrets in many places which would be impossible for a male detective." A criminal may not share his secrets with a male detective, but he would with his wife or mistress...and a woman detective would be able to befriend those wives and girlfriends and gain their confidence. She continued that men easily would become braggarts when they are around women who encourage them to boast. Kate also noted, women have an eye for detail and are excellent observers.

He asked for a day to debate the matter in private - she almost argued again but agreed to return the following day...when Pinkerton signed her up officially as the first female detective in history.

Pinkerton soon had a chance to put Warne to the test. In 1858, Warne was involved in the case of Adams Express Company embezzlements, where she was successfully able to bring herself into the confidence of the wife of the prime suspect, Mr. Maroney. She thereby acquired valuable evidence leading to the husband's conviction, ultimately resulting in the return of over $39,000 of the $50,000 he had stolen.

Because of her good work over those first few years, Allan Pinkerton put Warne in charge of his new Female Detective Bureau in 1860, opening the ranks to additional women that she would train and assign to cases. One such pupil, Merry Johnson, was supremely gifted, with Kate sometimes wondering who was teaching who in their lessons she was so adept and offered up alternate ideas.

In early 1861 Warne was instrumental in uncovering a plot to assassinate President-Elect Abraham Lincoln. The assassination was to take place as Lincoln was making his way to Washington DC by train. Warne was a big part of his protection detail, coming up with disguises for herself, Lincoln, Pinkerton and others as the train left Harrisburg Pennsylvania. Warne remained awake the entirety of the night's voyage into Washington, watching over Lincoln, leading some to theorize that Pinkerton came up with the company slogan "we never sleep" due to her actions that night.

Throughout the war Warne was one of the agents selected to join Pinkerton as part of the covert war intelligence agency, working out of Ohio. After the war she was part of a few high profile cases as well in addition to coordinating the female detectives within the agency.

While investigating a case on Jan 28, 1868 in Chicago Kate was shot by a suspect, she survived long enough for Allan Pinkerton to find her, before succumbing to her wounds. However, much to her shock, she woke up again some time later, whole and healthy once more. Pinkerton was not as surprised about that as she was - as it turned out in addition to being a detective he also happened to be a member of a secret organization known as the Watchers. His job as a Watcher was to watch and record the history of people who happened to be Immortal - and as it turned out, Kate herself was one of them. He explained to her what he knew of Immortals, and also asked her to keep the secret of the Watchers as most immortals did not know of them. He also warned her of a rogue faction of Watchers who called themselves Hunters who had turned on their training and tried to kill Immortals, believing them all to be evil and a threat to mortals.

Pinkerton put her into contact with an Immortal he was familiar with that went by the name of Cass Amador. He then took care of the arrangements for her "burial" placing her in the family plot with a provision in his will that her site was never to be sold and always taken care of.

Now officially dead, Kate made her way to Coshocton County, Ohio where Cass wasn't entirely expecting her - he had believed he had stayed under the radar from the Watchers and Kate assured him that only Pinkerton and another man she did not know, presumably Cass's current Watcher, knew where they were. Still, he agreed to take her on as a student, and the two fell into a comfortable partnership. Cass was working as a farmer, and though she had lived in cities if not on the move for most of her adult life, Kate had, once upon a time, lived in a small village and was not unaccustomed to the hard work of the life of a farmer.

She was aware of and supported his attempt at starting his Guardian organization, even considered herself a member, though it never got very far during her time with him. An alliance with the Watchers difficult due to the politics in their upper levels, and without the alliance the scope was limited. Still, she would share information on Hunters with those who had signed on as she gained it and offer shelter to any Immortal in need of it as she came across them.

She and Cass stayed together for several years before parting amicably, with him staying in the United States and her traveling to Europe for the first time. She joined various women's rights organizations in Europe and then in the United States upon her return in the early 1900's, keeping under the radar due to her immortality but providing critical support to the visible leaders. She returned to Chicago after World War One to pay her respects to Allan Pinkterton who had died some twenty years after her mortal death. She did not approve of the direction subsequent leadership had taken the agency after his death, so although she toyed with the idea of joining up again in the end she did not.
World War Two saw her back in Europe as part of the French Resistance. During the 1950s and 1960s she was back in the United States spending time in the south, lending her aid to African American efforts for Civil Rights. Always careful to be the supporter, stepping in to use her privilege as a white woman only when needed.

On a personal level she became close with a young woman named Dorothy. She was married and had given birth to a son, Elijah, though she eventually confided in Kate that she wasn't really in love with her husband, Raymond, nor he with her. Well, attracted to was perhaps more accurate, and romantic love wasn't something they shared either, though there was a deep affection. In reality they both were more interested in members of their own sex though that was a particularly difficult thing for anyone in the South but especially for African Americans.

Kate was always much more married to a cause or a job and hadn't really felt the need to become involved with anyone too often, though she would take a lover here and there, finding women more preferable to men. Dorothy was a different story and for perhaps the first time in her life she found herself in love.

Wanting a little more freedom to live openly, the foursome moved to San Francisco around 1970. Raymond would bring home boyfriends from time to time, though any that balked at Dorothy and Kate being there, or didn't like Elijah, didn't last. They were far from a conventional family but they were happy.

In the 1980s they had moved to New York were, unfortunately, the AIDS Epidemic had began to ravage the LGBT community. Though not versed in medicine in any way, something she would berate herself for, she split her time between caring for the people abandoned by society and even their families, and helping to advocate for those lost in the hopes that there would be a better future in addition to her duties with her family.
Sadly, Raymond contracted the disease at some point in the mid 80s and passed in 1991 about a month before Freddie Mercury of the band Queen also succumbed. Not too long after that Kate hit the point of burn out and she and Dorothy, now 51, retired to South Carolina. Elijah, now in his late 20s, kept in contact and visited from time to time but was busy with his own life.

Kate hadn't really been interested in the quiet life before, always looking for the next case or cause, but spending time with Dorothy became the most important thing to her now, especially since they had lost Raymond. She took to gardening but wasn't very good at it, much to Dorothy's delight. Allan Pinkerton had written several novels telling of the "exploits" of his detectives (including her) which gave her the idea to begin writing novels herself under a (sadly male because "no one wants to read mysteries by women") pseudonym.

Things were good until late 1999 early 2000 when Dorothy began to feel unwell. It took entirely too long to find a doctor that would take them seriously and actually examine her and the pair was devastated when they learned she had cancer and it had progressed to the point that there was really nothing to be done but making Dorothy comfortable for however long she had left.

An offhand comment by the doctor that did eventually diagnose Dorothy made something sit up and take notice within Kate - there had been an uptick in cancers in their area. And so, even as she was taking care and setting things up for her partner, Kate began investigating. Elijah came to visit more often and chided Kate for splitting her time. Dorothy tried to level things out between them by reminding them both that one of the things she loved most about Kate was her tenacity and dedication to a cause. And, that if something had caused her and others to be sick, they should do something about it.

Dorothy passed in April of 2001, and Kate threw herself fully into the work of finding out what had happened and holding someone accountable. In the end she learned it was a local company illegally dumping waste containing carcinogens that had seeped into the water. The case never saw a courtroom however as in June of 2002 everyone began falling ill with a flu virus. Almost overnight the remaining people Kate knew all passed away. She set to work burying as many as she could before strange dreams began to draw her west - one to an old woman in a corn field, the other to what seemed to be a man in Vegas. The woman offered peace though cautioned there would be hard work ahead. The man offered law and order - stability and holding people accountable for their actions.
Kate fell in with a handful of people making their way westward, even became a leader as the group grew. She lamented the fact that she didn't have the chance to try and find Elijah they hadn't spoken since Dorothy's funeral and she wasn't entirely certain where he was at the moment. She also was pretty sure he wouldn't be happy to see her, in part for the same reason she knew he wouldn't have died in the epidemic. At least not permanently.

The group she was with arrived in Boulder in early August. While the rest of the group she was with were settling in, Kate ended up speaking with an Immortal going by the name of Adam Pierson. "Methos, I presume?" she asked, her lips quirking as his own turned wryly up at the corners. She'd heard of him, of course, and since she could now actually feel some heaviness to certain quickenings (which she assumed was often age or perhaps they had been a head hunter) and that coupled with the tongue-in-cheek use of Adam gave her a hunch. He confirmed that that was indeed his real name and he nodded when she shared hers - Kate Warne, Pinkerton Detective was mostly lost to history even around Chicago but some knew of her and her exploits before becoming Immortal.

She offered him a proposition - though she had come to Boulder and believed herself to be mostly a good person, she also knew that she'd have no issue infiltrating Vegas to gather information - something Boulder would need. The only hitch was Flagg himself, which they both agreed had strange powers and could potentially know she was there to spy. To counter that, she did say she never truly said yes or no to either dream and would be straight forward with him if asked - she was there in Vegas to see what it was like. She might stay, she might not. She knew the risks and wouldn't back down now anymore than she had in the past.

She arrived in Vegas a few days later.