Boston girl Faith Lehane drifted into Sunnydale several years ago, called as a Slayer following the death of Kendra, but fresh from losing her Watcher to the demon Kakistos. The bad girl routine quickly divided opinion about her amongst Buffy and her friends, more so when she accidentally killed a man and covered it up, and when the evil Mayor of Sunnydale seduced Faith with promises of power and brought her over to the dark side, Buffy knew her greatest ally was now her worst enemy. After a titanic fight, Faith was wounded and slipped into a coma...
... waking almost nine months later to take another shot at destroying Buffy. When that failed, she fled to LA where Wolfram & Hart were only too glad to snap up her services and give her a new mission - kill Angel. Facing off against the only man who'd ever tried to help her proved too much for Faith, who begged him to end her wretched life - but he refused, and after some soul searching, she surprised everyone when she gave herself up to the authorities to face jail for her crimes.

Busted out a few years later to help take down Angel, who'd lost his soul and gone on the rampage as Angelus, Faith almost fell but managed to return the favour to Angel at last - they'd saved each other now, they were even. Showing up in Cleveland to help Buffy fight off a kidnap attempt against Dawn, Faith knew a lot more than she was letting on and was forced to move on following the events of 'Cradle,' which left Dawn dead and Faith blamed for it by Buffy.

     
 
 
     

Faith picked up a temp job at Webb Researching, just looking for some way to pay the bills while she kept up the slaying by night, but it didn't take long for her to discover that her boss, Pryor, knew all about vampires, demons and everything else, and that  he was just as committed to fighting back the forces of darkness as she was!
Faith also earned a new fan in Pryor's assistant, the bubbly young Noa, who quickly came to idolise her. Settling down to work, Faith battled all manner of foes but remained unaware of Jon Quinn, the detective on her trail following her murders in Sunnydale - but with Quinn actually working for shady military unit The Initiative, his true motivations were a mystery to all until he finally tried to arrest Faith...
With aid from the mysterious Gabriel turning out to be far from what it seemed, Faith was left in a state of disarray when she realised she was being used, a tool to make sure destiny followed its correct path - a path that was jeapordised when she was trapped in a vicious gladiatorial arena with her old Slayer colleague Vi by the rogue warlock Boone.
     
 
 
     

With Gabriel's help Faith was able to escape, but Gabriel gave his life to save her, sending Faith back to NY alone, where she crash-landed into an asylum run by Dr. Alexandra Salus, a woman with plenty of secrets of her own. With Faith's murderous past revealed to her team as they tried to revive her, the homeless Faith was offered a job at the Asylum by a sympathetic Alex.
However, an unexpected side effect of Faith's return from the Arena was the loss of all her Slayer powers - and the creation of an evil, sadistic mirror version of her, which promptly began a reign of terror against Faith and her friends, with the de-powered Faith struggling to defeat her. Evil Faith also put Vi through a horrific ordeal of torture lasting several weeks, leaving Vi in intensive care and Faith with another ally unable to help her.
The discovery of the Gateway in the Asylum's depths deepened the mystery - as did Faith's sudden appointment as 'Warden' of the ancient structure, believed to be some kind of mystical transportation device allowing passage to other worlds and dimensions. This is something Evil Faith used to her benefit when she launched a full-scale assault on the Asylum, fighting past Faith and tossing Alex through the Gateway, escaping to fight another day...
     
 
 
     

Evil Faith had another aim in mind - the resurrection of Mayor Wilkins! Wilkins wasted no time in consolidating his position, re-activating Faith's Most Wanted status, allying himself with the demonic leaders of the Church of Hessionism, using his influence to keep pressure on the team and recruiting new allies like the bitter rogue Slayer Ambrosia and the Darkling to his cause.
With the return of Dawn Summers giving the Mayor access to the power he needed to warp the Gateway to his own ends, it all came down to a climactic showdown at the Church himself - Evil Faith was defeated and Faith's Slayer powers restored, but nobody noticed Wilkins slip away in the aftermath - and get himself elected the new Mayor of New York!
Noa was also a victim of the fight, but she's still alive - somewhere! Trapped in a foreign dimension where she has the power to walk again, the team have been searching for her since that fateful night, even as the Mayor continues to expand his influence and power...