In episode 4.20 "Taxi", Mac becomes upset when he learns that Reed has a source close to the Cabbie Killer and won't divulge it. When Mac goes to talk to him about his source, he finds Reed's backpack on the floor of his apartment hallway, and his keys still in the lock. Back at the lab, he realizes that Reed has been kidnapped by his source—the Cabbie Killer himself. Mac is extremely worried for his stepson's life. Through posts on Reed's blog, the team is able to locate the Cabbie Killer and the now injured Reed. Mac stays with Reed at the hospital, and after catching the Cabbie Killer, takes him home.