Doctor Who: Every Modern Companion's DEFINITIVE Episode

Interestingly, my pick for Ruby's most quintessential episode doesn't come from the series in which she travels with the Doctor. She does get some development in 'series one', but much like other companions covered in this list, she spends most of her run as a mystery box with a particularly underwhelming reveal. Lucky Day is the only story where we get to see Ruby divorced from this plot and can finally see here as her own person, heading up a Doctor-lite episode that devotes its runtime to exploring what life is like for companions after travelling in the TARDIS. 

From the off, we see Ruby is no longer the same person she was when she started travelling. She is more alert, more confident, and more willing to jump into action when something isn't right, even going so far as to take command of a room as the Doctor would. But this episode zones in on a very understandable side effect of returning to normal life after experiencing the Doctor's world. One that we haven't seen with previous retired but still earthbound companions: Ruby is paranoid - she's trained herself to analyse the threats in the environment around her to a degree that is no longer necessary, and it's made her a little inaccessible. She struggles to connect with others as she looks at the world through a different lens. 

Ruby's unique struggles distinguish this story to others with similar ex-companion storylines like School Reunion, The Sontaran Strategem and Power of the Doctor. I also really like that the episode has an antagonist that directly ties into this exploration of Ruby with Conrad actively exploiting and weaponising Ruby's trauma. Think Tank and the way they use Ruby in this story allows us to really explore the ways in which life with the Doctor can lead to changes that aren't always for the better, and how it's often up to other friends of the Doctor, in this case Kate, to handle companion aftercare. It's a great story for UNIT, and for once, Kate isn't possessed by an evil force here (though that doesn't stop her from slipping further into her war crimes era). 

We also get to see snippets of Ruby's family life, and her relationship with her birth mother, juggled alongside her adoptive family. This is the only story we get to properly see the aftermath of series one, and these charming scenes are some small solace for Empire of Death's terrible handling of Ruby's parentage mystery. It's a shame she didn't get a full series unburdened by her narrative baggage.