The Biochemist goes on different excursions in her TARDIS than the Doctor does in his. Fewer historical landmarks; more extinct species of flora and fauna, natural disasters, and worlds where no human had ever set foot. Oh, and then research facilities. Lots of research facilities.

Her companions are memorable, too. A father figure, proud of everything she does. A dark-haired, closed-down warrior, never backing away from even the most fearsome creatures they encounter. A young woman with a secret past, brash confidence barely masking uncertainty and vulnerability. A handsome soldier who brings her whatever she asks for, if he knows what that is, and what it looks like, and where he can find it.

Truth be told, though they each have their strengths in the field, they're all pretty rubbish in the lab.

There used to be another. Sometimes, there still is, just there out of the corner of her eye, just audible over everybody else. Sometimes, when there's nobody awake but her and the TARDIS, and she's running her hands over the controls like someone who has all the time in the world, she feels the pleased hum of her ship, closes her eyes and sees its heart, the other half of her. The Biochemist and the Engineer, saving the universe one discovery at a time.

She can always hear him, and she always listens, and it's saved her life more than once.

On a desert island is a box. Inside that box is the TARDIS. But the TARDIS itself is always a desert island in the end, always lonely.

And she always wakes up, and the TARDIS is always gone, but...

On the floor of the ocean is a box. Inside that box are the remains of her last purely hopeful moment. Inside that box is a past that can never be recaptured, a future blasted into so many shards of glass, but if she had it to do over again, that box, she would do just what she had done.

She would live physically unscathed, keeping the damage where he couldn't see it.

She would be fine—better than fine, she'd be amazing.

And sometimes, when she's running her hands over the glass of his hyperbaric chamber like time has stopped existing, she almost imagines she'll be able to fool him into believing that when he wakes up.

Almost imagines that she can fool herself into believing it, too.