She was played by Lauren Stamile.
Kiersten Joyce is a detective for the Organized Crime Task Force (OCTF), as well as the girlfriend of Nigel, a notorious car thief. She worked with Dan and Jack on the case regarding stolen classic cars, which led them to Nigel's warehouse. Kiersten was revealed as a villainess when she was shown on the phone with Nigel, warning him that his warehouse had been found, officially revealing her role in the thefts. While on a dinner date with Jack, Kiersten is informed by Nigel that she had to take Jack to him, which she does when she holds him at gunpoint. Despite Jack's efforts to fight Kiersten, the villainess sprays him with mace and handcuffs him.
Kiersten took Jack to Nigel's warehouse, but after doing so, Nigel decides to not only kill Jack, but Kiersten as well, mainly out of anger over her hookups with various cops as part of her cover. After they are both saved by Dan, who crashes his car into the warehouse, the evil Kiersten attempted to escape, only to be taken down by Jack. Kiersten is later arrested for her role in the thefts.