This is a story about the in-betweens of the Doctor and Donna's adventures. Not any specific adventures, mind you. I doubt there will be any spoilers for Season 4 (although I did manage to catch the first episode—David Tennant and Catherine Tate were born to act together, that's all I'm saying) and I know there won't be any in this particular chapter. This chapter is a short little introductory thing, mostly because if the whole story is put down in one big chunk it doesn't flow quite right.
Disclaimer: Doctor Who: Not Mine.
The Doctor lunged into the TARDIS, just managing to close the doors before a horde of angry aliens made it inside. He staggered up to the console, initiating the dematerialization sequence while studiously avoiding Donna's face. He succeeded for a whole thirty seconds, at which point he made the mistake of looking up to check a monitor and subsequently caught Donna's eye. Approximately seven seconds after that, they both burst into uproarious laughter.
For the Doctor, this was the best part of traveling with Donna. They raced across time and space, had shenanigans, then came back to the TARDIS and had a laugh at the absurdity of their life in general. It was the perfect platonic relationship, and the Doctor loved it.
Best mates for an indeterminate amount of time, as he liked to say, mostly to avoid the "forever" that he felt had doomed he and Rose apart. Never tempt fate.
For Donna, the best part was what came after the obligatory laugh at life. Not that she didn't love running around the universe and getting into trouble--she did, probably more so than was healthy--but the real good times, the ones she would always remember after this chapter of her life had ended, happened after the danger was over. She would go take a shower, because they did a lot of running and running made her sweaty which made her feel gross. There wasn't a faucet with knobs that you could turn in the shower, but the TARDIS always got the water flow and temperature just right when she asked, which she had found a little alarming until the Doctor had explained that for all intents and purposes, the TARDIS was a girl. After her ritual shower (perfect every time), she would re-dress in a clean t-shirt and slacks and search out the Doctor.
The first time this happened, he was not prepared.