Writer and executive producer Steven Moffat on just why this episode is big for fans:
"They've [the Ponds] become extremely good at being Doctor Who's companions. They've become an expert at it. They're like the A-team when they arrive on the planet; they know exactly what to do. . . . When you start that story again [with a new companion], you have someone who is brand-new at it, and it's a fresh take on the Doctor. Somebody who still believes in him, who doesn't know he has two hearts yet, who doesn't know any of the information."