During the first few seasons, McGee was portrayed as timid and inexperienced. In the Season 3 episode "Probie", he was visibly shaken after killing his first suspect, even though it was in self-defense and his teammates backed him in the subsequent investigation. When questioned about McGee's guilt, Gibbs commented that McGee "doesn't know how to lie". His character was almost entirely altered by episode 6.12 "Caged", evolving into a bolder and more assertive character. Following Gibbs' brief retirement and Tony's subsequent promotion he becomes the senior field agent. He takes on the role very seriously, gaining Tony's respect. Tony later stops calling him "Probie" and starts calling him "Tim". He is shown to be very protective of his younger sister, Sarah, especially when she shows up after apparently committing a murder. He hides the case from his team to protect her while simultaneously launching an investigation into the case in the episode "Twisted Sister".