The story of the best 'Doctor Who' companion of the 1980's is (like Ace herself) cute, complicated, and straightforward all at once.
The Doctor chanced across a girl in the distant future, working at an ice themed restaurant on the ice-y ice planet Svartos.
Calling herself only 'Ace', Dorothy Gale McShane had arrived on Ice World due to an unpredictable 'time storm' following an experiment with her home-made explosives in the London suburb of Perivale in the year 1987. In other words, she arrived with a bang.
She was mouthy, spunky, quick to action, and didn't give a toss if her room was neat or her armpits were shaved. At 13 years old, I took quite a shine to Ace. She was 16 but she told everybody she was 18, and she was TOUGH. Maybe TOO tough for the likes of me, but hey, it was my fantasy, right? (Sophie Aldred may or may not have taken out a restraining order prohibiting me from setting foot on her continent. What of it?) She called the people she didn't like 'toerags' and hit Daleks with a bat and she had a giant tapedeck and a knapsack full of fricking grenades! Find me a teen boy who thinks ANY of that is a bad idea.
Ace took up with the Doctor, but I would venture to say she was his last onscreen female companion where there unequivocally ISN'T anything romantic happening. At least, they aren't kissing! (He's too old for her anyways, Ace would be better off with someone younger... skinnier... Canadian.)
They are in CAHOOTS, though. It's a mentor/student thing for "The Professor" and his friend "Ace", which grows closer over time until they are more like surrogate family. With all the emotional turmoil that entails. He needed a daughter and she needed a daddy.
So what if they're not the same species?
He's got the brains, and she's got the bombs, and they've both got issues like tissues.
Leaping for cover, snarling in frustration, cruising for boys, leading a rebellion, or holding aloft the sword Excalibur, Ace is always on the move. "Sometimes I travel so fast I don't exist." she once observed.
Two TV years together and Ace is the single companion with no televised departure. In many ways, she never left. In many other ways, she's left a lot:
Paul Cornell wrote a heated argument into the novel 'Love and War' where Ace finally storms out of the Doctor's life at age 26. She spends three years as a Space Marine, having wanton affairs and killing Daleks by her lonesome, then storms back into the TARDIS at 29 along with his new companion, Benny. (More on HER later.)
There's a comic where Ace dies. (Ask me if I think it's canonical... don't bother, I haven't read it, but it ISN'T. Or she got better. Or it was a parallel universe. Quit asking!)
There's a cool audio adventure (Death Comes To Time) where Ace's in training to become a Time Lord because their race is nearing extinction. I am very fond of it and it has Stephen Fry & Anthony Head in it, too. Which is even cooler!
There's a novel by Kate Orman (Set Piece) where at the end an Ace in her (thirties?) becomes a solo adventurer guarding a dimensional Rift near Paris on a time-travelling motorcycle. (This is supported on-screen during 'Silver Nemesis' by a painting young Ace discovered. See, she'd pose for it in 1880's France in her own personal future.) The rift guardian bit is kind of 'Torchwoody', but I like it anyway.
I hear in Cornell's 'Happy Endings' Ace might get married. (It was written 14 years ago, but it takes place in 2010. I better see how THAT turned out!)
You kids with your baggy pants and your tongue studs can keep your Roses and your Marthas. As the 7th Doctor once said: 'Exotic alien swords are hard to come by... Aces are RARE.'
If I have been too effusive in my praise of a fictional punk 80's kid from a cancelled TV show no one else was watching then so be it: Ace is wicked!
(And for the record, yes, I enjoy it when my wife wears a ponytail and calls me a 'toerag'.)