The Doctor Who series 10 opener finds the Doctor and the Tardis grounded (give or take one or two quick trips to the other end of the universe) as the Time Lord fulfils a pledge to guard a secret and keep his true identity under wraps.
"No-one can know about me… I cant do that any more, I promised," he says. It's a responsibility he clearly takes very seriously.
But as the episode comes to a close, the Doctor has a change of heart, meeting his new companion Bill outside with the Tardis.
"What changed your mind?”
she asks him.
"Time. And relative dimension in space,” says the Doctor, who has clearly been doing some travelling since his last meeting with Bill.
“It means... what the hell!"
It's an important moment that kicks off a new series of adventures for the Doctor and his latest companion and reminds us that the Time Lord is not always one to follow the rules. But there's some added significance to those words and that situation, too, which may just resonate with fans of another time-travelling franchise.
You see, this exchange echoes very closely one between Doctor Emmett Brown and Marty McFly in Back to the Future...
In 1955, when Marty tries to give Doc Brown a letter explaining how to avoid his untimely death in the future, the Doc is outraged, tearing it up rather than bear the responsibility of the impact it might have on the wider timeline.
But when Marty returns to 1985 only to find that the Doc has taped the letter back together and saved his life by buying himself a bullet-proof vest, Marty asks him what changed his mind…
“What about all that talk about screwing up future events, the space time continuum?” he asks.
“Well,” says the Doc, “I figured... what the hell!”