Well, the Doctor’s back, and he needs a new companion. That means we get a new one in the form of Martha Jones.
And the producers were totally hoping you didn’t notice Freema Agyeman played a different character who got killed on the show not that long ago.
Now, near as I can make out, the Tenth Doctor had three companions, and Martha is perhaps the least impressive of the three. No one was going to go bigger than the outsized personality of Donna Noble and Rose was, of course, as much a love interest as a companion. Martha is, well, the rebound relationship. That doesn’t mean she’s a bad character. Quite frankly, I love what they did with her as an introduction. She may be the first companion in ages to actually show real skepticism of whatever the Doctor is saying and doing, right down to the way the Doctor just won’t give a name beyond his usual alias as “John Smith”.
She also has a larger family than Rose did, a more normal one even if her parents Clive and Florience are divorced and her brother Leo and sister Tish seem to rely on Martha to be the family peacemaker. Also, she’s a doctor/medical student herself, someone who can keep a secret when, examining the Doctor in a hospital, notices he has two hearts.
What really impresses the Doctor is she asks good questions and doesn’t show fear unlike everyone else in the hospital when it first starts raining hard exclusively on the building and then the rain goes up instead of down and then the whole building gets zapped to the moon. Also, the space cops show up.
That would be the Judoon. They look like Rhino Men.
They are very…legally minded. Fighting back is a bad idea on many levels. But they are looking for a murderer who isn’t human, and there’s a good chance they’ll take out everyone there for housing a fugitive.
Point is, Martha helps the Doctor catch a shapeshifting assassin who assimilated some human DNA to pass as human until the Doctor tricked her into assimilating some of his own. Then she can’t pass for human anymore. The rest comes down to timing to make sure the Doctor shuts off her rigged MRI machine that would kill everyone, human or alien, in the hospital plus half the population of Earth before the Judoon return the hospital to where they found it and everyone dies from lack of air.
That all works, so the Doctor offers to take Martha on one trip as a “thank you”. She’s pretty skeptical of it all, but she adjusts quickly, and when has the Doctor ever gotten someone back after just one trip?
Though he does go out of his way to say Martha is not a replacement for Rose. So, you know, that “rebound relationship” remark above might not have been that much of a joke…