10 Best "Everything You Know Is A Lie" Moments In Doctor Who

After being flung to the end of the universe, the Doctor, Martha, and Captain Jack find themselves surrounded by the last surviving dregs of the human race.

Among them is Professor Yana, an old scientist attempting to get the humans to Utopia, where they will be safe. Supposedly. But Yana has to be a good guy, doesn't he? He's played by Derek Jacobi. Look how kind his face is!

Unfortunately, Jacobi is such a good actor that he even fooled the Doctor, as revealed when Yana opens a pocket watch, bringing his memories, and his true identity, back to him.

He is the Master.

Jacobi's transformation from kind old man to power-hungry villain is sensational - it's like he just flips a switch - and the build-up to the reveal is as tense as you could imagine.

You actually feel sorry for Yana at first as he breaks down in front of Martha and Chantho, before your sympathy gradually fades as it becomes apparent that this deranged killer is not someone you should be rooting for.

This moment is often cited as one of Who's great plot twists for a reason, and it still holds up all these years later.