Doctor Who: 10 Times The Doctor Lost

10. When Bill Potts Was Turned Into A Cyberman

In an amazingly taut scene near the start of Peter Capaldi's last series finale, companion Bill Potts is shot through the chest - with a bullet that leaves behind a massive, gaping hole - and drops to the ground.

Here, we get to see just how powerless the Doctor is against something as simple as a gun, and for all his talk about saving the universe and doing the right thing, he can't stop one of his companions from just... being shot. And while Bill's death seems like a bad enough way to start the episode off, things only get worse from here.

Bill's body is taken by a group of sinister-looking doctors, who escort her down to the lower levels of the ship. As things unravel, we learn that these doctors are early descendants of the emotionless Cybermen, and that Bill - in order to restore her life - has been converted into one of them.

It's a nasty turn of events for the kind-hearted Bill to be put through, and this whole situation can be pinned directly on the Doctor himself. He trusted Missy to handle this particular mission, which led to things getting out of hand, which led to Bill taking a bullet, which led to her becoming a Cyberman. The Doctor's overconfidence got the better of him and he messed up, big time, and he only had himself to blame.