So Katarina dies suddenly and later on in the same episode of the mammoth The Daleks’ Master Plan we are introduced to the next new companion, Sara Kingdom. At first a foe, she befriends the Doctor and Steven and travels with them through time and space in the TARDIS their epic battle against the Daleks (as well as a not-so-epic Christmas day adventure, The Feast of Steven in the midst of the story). And the audience is probably thinking, right, so here’s the new companion, she’ll survive this story and continue to travel with the Doctor and Steven because there’s no way they are going to kill another companion. And the audience is wrong once again, as Sara is tragically killed at the end of the 12 part story. And it is a smidgen more effective departure than Katarina’s (itself very effective) because the shock of having the guts to kill off another companion shortly after doing it the first time is still there - and we feel it a bit more because we get to know and invest in the character a lot more - as short as Sara’s run is, it is still twice as long as Katarina’s, with much more focus on the character in those 9 episodes versus the five that Katarina was in.

Some may quibble with Sara Kingdom’s inclusion as a companion on the list since she didn’t appear in more than one televised story - but fandom has long deemed her to be a companion because she traveled in the TARDIS as a companion for several weeks and arguably The Feast of Steven is a separate adventure (televised in the midst of The Daleks’ Master Plan, it has nothing to do with the plot of that story, which, when the BBC attempted to sell it abroad, did so as an 11-part story without The Feast of Steven). Sara’s photographic appearance in The Day of the Doctor (amongst a host of other companions) and the fact that she’s featured as a companion in several Big Finish audios I think cements her status as a companion, if it was ever in doubt. As such, she is included in this list and her departure squeaks into the top 15.