S6, E14: While Jack fights for his life in the hospital, the team searches for Diana (guest star Daveigh Chase - Big Love), a 16-year-old heart transplant patient who disappeared after cheerleading practice. The team tries to determine if her curiosity about the boy whose heart saved her life may be the reason for her disappearance. And Brian Donovan (recurring guest star Adam Kaufman), the father of Samantha's unborn baby, shows up.