Continuing the re-reading... as is probably obvious from the title, this is part of Anne McCaffrey's Ship series.
The brain is Cari and the brawn Keff. They have a wonderful relationship that is just really fun to watch. She's the princess and he's her knight and they have this whole pretend thing going on between them all the time.
They work for a different organization or part of the government or something than most of the rest of the ships in the series. So instead of getting sent on errand type missions they're explorers and go out looking for new planets and sentient species.
Of course they find a couple and nothing is as it seems and they have to figure it all out. And there's frog princes and magicians and it all fits with the way they interact with each other.
I just really like the relationship in this one. She's always wanting to keep him safe and he wants to go on "quests" for her.