Lisa Halle is a mortal convicted murderer, she murdered her husband Martin Halle, who was a phychiatrist. She has a history of deceiving and using people to her advantage and eventually murdering them. James Horton, a former Watcher turned Hunter, had his people break her out of prison. They offered her money, a new face, and freedom in exchange for Duncan MacLeod's death. They altered her to resemble Tessa Noël, and made sure she was educated in the art world so she would make a creditable foil.
Once she had insinuated herself into MacLeod's life, she pretended to be freaked out by photos of Tessa and just how much she resembled her, and angry MacLeod wanted a Tessa retread and not her. She ran out on him only to be 'captured' by Horton's people. MacLeod, however, had begun to suspect that she was a plant, but being MacLeod he had to save her anyway.
After her rescue, she insisted they go to visit Tessa's grave, to remind him she was dead. Duncan then asked her what she looked like before her surgery. Knowing she was blown she spun a lie about a six year old son, Mark, being held by Horton. She pulled a gun on him saying she was once married to a psychiatrist who kept trying to understand her up until the day she killed him.
He named her a sociopath, and she acknowledged that, and he informed her the gun was empty . After MacLeod faked his death by her hands to draw Horton out, Horton shot her, and pushed her into MacLeod's arms. She died on Tessa's grave