Doctor Who: Every Modern Companion's DEFINITIVE Episode

The first half of series one is all about an 'ordinary' girl being dragged into the Doctor's world. Sure, we return home for the Slitheen two-parter, but it's still firmly an 'alien' story. Father’s Day, at the midpoint of the series, is the first time we see Nine pulled into Rose's world. Straight off the bat, it's Rose who sets the wheels of the story in motion by saving Pete from his pre-determined death, and her additional motivation for travelling through time is revealed. Not only does this understandable betrayal of the Doctor's rules give Rose more depth, it puts her and the Doctor at significant odds for the first time, with him even going so far as to question if he's made a mistake in travelling with Rose. 

Rose isn't a passenger in this story, the entire thing orbits around her as she deals with the consequences of 'breaking time', trying to juggle the alien threat, the Doctor's anger, terrified wedding guests, her own mother, and the fact that her late father is standing right in front of her. To shift the spotlight even more towards Rose, the Doctor is gobbled up by a gargoyle and killed halfway through the episode, leaving the finale to hinge not on the Doctor's heroics, but on a difficult and very human choice for Rose and Pete. 

Rose isn't shown as particularly selfless or heroic in this story - she's drawn to act selfishly throughout, trying to undo the 'unfair' loss she's suffered. Her complexity really starts to show itself here, and Piper's acting chops in this one are phenomenal, especially in her one-on-one scenes with Shaun Dingwall. The story also gives her emotional closure, even though Pete still dies. She gets to meet Pete, and Pete, in turn, gets to be a father to her and sacrifice his life to protect her. She also manages to change time, just a little, as Pete no longer faces his death alone. 

The dynamics introduced in this episode, the first to truly focus properly on Rose's family, would become a backbone of the first two seasons, doing a lot of early legwork to make the introduction of 'Parallel Pete' work in series two. It's a deeply underrated and top notch story that I don't believe enough people credit with making Rose Tyler the character she is.