Doctor Who: 10 Biggest Lies The Doctor Has Ever Told
7. Breaking Ace's Faith In Him
In The Curse of Fenric, the Seventh Doctor and Ace go up against Fenric and the Ancient One, to incredibly powerful beings who seek to destroy everything. There is a catch during their final confrontation: Ace's unwavering belief in the Doctor's infallibility.
This was an early adventure for her, so she saw the Doctor as a mentor and someone who was to be trusted absolutely. This presented a problem for the Doctor, as her faith creates a barrier in the room that they are in, making the Ancient One powerless to act against Fenric. He devises a cruel yet effective way of dealing with this. Fenric threatens Ace's life, saying he will kill her if the Doctor doesn't give him what he needs. The Doctor answers 'kill her'.
He proceeds to scoff about what a failure she is, that he would never normally take in a street kid like her and that he was using her the whole time. This crushes her, breaking her walls down. The Ancient One moves forward quickly and the Doctor rushes her out, allowing the two other monsters to destroy each other. Though he does explain to her why he lied the way that he did, she is badly shaken by the experience.