10 Dropped Doctor Who Plot Threads We'll Never Get Answers To

In the Series 1 episode Father's Day, Rose alters a fixed point in time when she stops her father, Pete, from dying in a car accident.

In response to her meddling, a group of winged creatures - Reapers - appear in the sky and start attacking people at random. The Doctor describes these creatures as bacteria being drawn to a wound, indicating that the Reapers are attracted to fixed points in time that have been messed with or changed in some way.

So isn't it pretty odd that we haven't seen the Reapers since this episode? The Doctor and his companions have tampered with fixed points in time on countless occasions since Father's Day, and yet, the Reapers haven't shown up to play.

There are plenty of theories as to why this might be - some speculate that the incident in Father's Day was unique, while others think that the Reapers themselves are rare beings who can't attend to every single crack in the universe's timeline.

But if we're being honest, the real reason why we've only seen them in one episode - and the reason why we'll probably never see them in another - is because it just isn't feasible (from a production or scriptwriting standpoint) to have to bring back the same monster over and over again whenever a story involves some time-meddling.