Martha’s no daredevil; she’s always been the sensible, cautious one in her family, the eldest daughter, the one with her head firmly screwed on. It’s just as well considering how scatter-brained her siblings and even her father can be. Her mum shouldn’t have to keep them in line all by herself, especially since her dad got involved with a younger woman. Mid-life crises are such a cliché.
But here she is, travelling the world on her own, risking her life to help the Doctor set right what the Master is intent on tearing apart. The whole world’s counting on her.