Zero has constructed something that homes in on cell phone calls. You must use this device to track down one of the cars on your client's list. However, the signal will go away after a bit, so you must hurry to each blip on your radar before it goes cold. At first, the blip will be red and will become white and will eventually start to disappear.
As you spot her car, an on-screen prompt will tell you to spin her around with the PIT maneuver from Driving School. As long as you don't destroy the car, you can stop it by any means. Once you do that, the driver will bail the car and run away. That's your cue to steal the car and drive it back to your garage in Doherty. Missions complete and $5000 and respect earned.