10 Doctor Who Characters Who Died For No Reason
4. Sara Kingdom (The Daleks' Master Plan)
Partially-missing First Doctor serial The Daleks' Master Plan features the death of short-term companion Sara Kingdom, and while it's certainly a horrific, memorable demise, it only happens because she doesn't listen to a basic instruction given by the Doctor, making the outcome feel highly frustrating.
In the final episode, the Doctor activates the Time Destructor, a superweapon that can drastically increase the flow of time. While doing so, he implores his companions Steven and Sara to head back to the TARDIS, out of the Time Destructor's reach. Steven obliges, but Sara instead decides to double back and help the Doctor, an act which seals her death. The Time Destructor ages her up significantly, making her frail and weak, before she finally turns into a pile of dust.
Sara's intentions were noble, sure, but the Doctor didn't even need her help - and as such, it felt like the serial had to dumb her down a little to make her go back for him, creating a weak excuse to kill her off.
Interestingly, there might even be some truth to this assessment. Sara was intended as a one-and-done companion, so her death had to happen no matter what - and this was clearly deemed the best way to do it.