I rewatched The Runaway Bride for timely reasons and was struck by how well it introduces the third season and several of its themes; I like it by itself (far more than The Christmas Invasion, actually), but as an overture to s3, it really shines.
The big picture versus the individual life: "it's like you said, Doctor," says Lance, Donna's deceitful fiance, "the big picture. Who cares about humans once you get how little they mean?"
Lance and the Empress of the Raccnoss, that very long lived creature with a space ship and designs on the planet and a habit of doing comedy routines, are a parody of the Companion and Doctor relationship as surely as Master and Lucy are going to be. Lance, like Lucy, gets "chosen" by an alien vastly older and superior in terms of experience and power, gets presented with "the big picture", concludes that there's no point to humanity and sells it out while seeing himself as the "consort" (while being really little more than a puppet, at least in Lance's case, as there is a bit more room for interpretation about what, if anything, the Master felt for Lucy). There is even that moment of play-acting; Lucy for Vivienne Rook, the reporter, Lance with the axe for Donna.
The Empress of the Raccnoss is a good old fashioned Who monster; wants to conquer the planet and eat the population (or, well, let it be eaten). At the same time, she's ancient (though not forever), the last of her kind - until for a very brief time, she's not anymore, and then she has to witness her kind dying all over again. Cackling monster that she is, she gets the harrowing "my children, my children" Niobe moment in the same sequence that showcases, for the first time in New Who, just how other the Doctor can be. Yes, Nine had the moment with the gun in Dalek and the anger in Parting of the Ways. But the former was clearly presented as a form of breakdown, and the later counteracted by the fact that when it came down to it, he couldn't commit the same act that had ended the Time War again. He couldn't. If not for Rose and the TARDIS coming back, the Daleks would have won; the fate of the galaxy very much rested on a literal dea ex machina, and I think the awareness of this very much contributed to what the tenth regeneration of the Doctor became. Because he didn't actually come into a similar situation through season 2, it was less obvious (you had the "I am so old now, I used to have so much mercy" moment in School Reunion, but season 2 by and large left it at such hints), but in The Runaway Bride, he is in that kind of situation again. The Raccnoss might not be the Daleks, but they do have the wiping out of the human race in mind.
It's a very skillfully constructed scene. All through the special, Donna has been referring to the Doctor as "Martian Boy" and he protested "I'm not from Mars", but he refuses to say where he does come from. Old Who watchers know, of course, but New Who watchers haven't heard the name of the planet on screen until this point, nor do they know anything of the Time Lords other than they fought the Daleks and the Doctor is the last one around. The Doctor offers to take the Empress and her children to an uninhabited planet; the Empress refuses, to no one's surprise, and does the usual villain gloating stick, which is where the "Martian" gag finally runs it course.
"My planet," says the Doctor, "is long since gone, but its memory lives on, and its name is Gallifrey."
Gallifrey. The first time it is said out loud in the New Who era, and the Empress recoils. "They killed all the Raccnoss", she screams about the inhabitants of that long gone planet. "I warned you," says the Doctor, and initializes the act that wipes out the last of the Raccnoss, accompagnied by water and fire which gives it a biblical aura. It's not, incidentally, the first time he commits on screen genocide - the Seventh Doctor did that, in Old Who, long before the Time War - but it's the first time he does so on the revived show, and the way he does underscores and brings out the frightening aspect of the Time Lords in general and the Doctor in particular in a way nothing before did. He isn't being gratitiously cruel here, and there is a very good reason for the act - obviously, letting the Raccnoss loose on the human race isn't the preferable option. But he is inhuman in more than one sense of the word. It's not an act of despair or rage; it's passing judgement on a devastating scale. Not coincidentally, a clip for this scene serves to illustrate the Doctor's frightening nature in Family of Blood when Tim opens the watch and asks "do you really want to face this?"
Now flash forward to the end of the season. The Master always served as the Doctor's shadow self and dark twin on the show, but they really emphasized it above and beyond there. During one of the few not-taunting moments, in reply to the Doctor's question, the Master says "I am a Time Lord; I have that right". We see him standing in the window of the Valiant at the end of Sound of Drums much in the way the camera shows the Doctor standing on the platform when dealing with the Raccnoss; looking down, dispensing Armageddon.
However, in The Runaway Bride, Donna ends this moment. Donna is in many ways the anti-Companion, if you look at the other New Who companions. (Old Who allows for some predecessors.) Her ending up on the TARDIS wasn't her choice, or the Doctor's; they are instantly appalled by each other; and Donna really isn't a big picture kind of girl, between having had a hangover when the Sycorax showed up and being scuba-diving in Spain during the Cybermen invasion, and having absolutely no interest in either. Her family doesn't angst and worry about her, her family had the wedding reception without her. Also? She doesn't need a mother to slap the Doctor, she does that herself, and is very much non impressed.
But that's just side. Donna and the Doctor start to bond on the rooftop after he saved her from the Santas and she missed her wedding; it's a poignant, quiet scene about lost dreams and shared coats (loved her "god, you're skinny!" reaction when he put said coat across her shoulders, btw), ending when he gets high-handed again and she not unreasonably asked him whether Rose ever punched him in the face. Donna's very non-specialness is the essence of her humanity. After the Santas attacked the reception, Donna says to the Doctor: "You're a doctor, people have been hurt, you can help." "Looking at the big picture here, Donna," he replies, trying to find out where the attack came from. "All the same," she insists. Which isn't just pointing towards Martha-the-doctor but towards what's important for the Doctor not to forget; not the big picture, but the invidual. Before the story is over, he gets presented with a ghastly version of big-pictureness, as mentioned above, and you know, he doesn't forget the individual, which is the difference between him and the Empress (or him and the Master, for that matter), and presumably what saves him from becoming either. The "I'm sorry" of this story is spoken as a moment of empathy for Donna, who at that point is about to realize what Lance did to her; the second time he says it, it's addressed to Donna again.
"I'm sorry I couldn't save him," him being Lance.
"He deserved it," Donna replies, looks at the Doctor and then adds, sadly, "no, he didn't." Does a man who gloated about his signicant other's pain and was ready to see the human race, well, decimated would be the wrong use of the word, so, let's say, killed off, deserve to die? Does he deserve to be saved? To be mourned? Well now.
Donna doesn't see the big picture, but she's courageous, she's fairly clear on people not deserving to die, even rotten ones, and most of all, she's clear on the Doctor not being just the guy who saves lives but someone who is scary as hell and needs to be stopped now and then. He invites her to come with him; she declines. The Doctor does what he usually does in this type of situations, says "okay" and tries to get away as fast as possible, but she stops him from going before she had her say. Does that sound familiar?
The show sometimes can handle the humanity-as-temperance-and-provider-of-HUMANITY thing rather badly; as in the Dalek-two parter in s3, which had a lot of interesting ideas but bad execution of same. It did, however, provide an important precedent of the Tenth Doctor's attempt to work with an arch nemesis and desperate need to believe in the possibility of change. When he goes for the Oncoming Storm aspect instead, you get chilling fates like those of the Family of Blood. The Runaway Bride pointed towards both aspects in the third season; the frightening ruthlessness as well as the ongoing ability to care and indeed the need to do so.
Lastly: loss as a theme. As a transition piece between seasons 2 and 3, the loss of Rose is one obvious element in The Runaway Bride, but I'm with
darthcorrie who argues
here that the loss of Rose is really just the surface; what the Doctor truly hasn't dealt with, and which will come to haunt him in the third season, is the loss of Gallifrey. Names are power, words are powerful, we learn in The Shakespeare Code. Gallifrey gets named out loud for the first time since it was destroyed in The Runaway Bride, in a context of devastation and judgement. Grief, says the Carrionate in The Shakespeare Code, grief unmeasurable, that's how we got in. That's how we returned. Grief and words. As in a ghost story, naming Gallifrey brings back the dead. Who else gets name-checked in The Runaway Bride? One Mr. Saxon, giving the order to fire at the Empress' ship, which destroys it and kills her, thus concluding what the Doctor started, that act that was simultanously saving humanity and committing genocide.
But Gallifrey wasn't a lost Eden, nor were the other Tiime Lords people who by and large got along well with the Doctor. The combination of words and grief continues in Gridlock when Martha makes the Doctor talk about his homeworld, and what he describes there is true, but only one aspect; the beauty of it. That other aspect, the terribilita, waits to make its appearance until the last three episodes, and of course, it's the Master who comes back, not Romana or, say, a Gallifreyan who wasn't exactly friends with the Doctor but not an enemy, either: it had to be that shadow self, the person he knew from the time he was eight, for all the centuries of his life. Ending in fire and loss and death and grief, all over again. The Empress, crying for her children; the Doctor, crying for the Master; opening and ending of the season.
But not quite. Because The Runaway Bride doesn't end there, it ends with Donna taking her leave, and Last of the Time Lord ends with Martha doing the same. "Will I see you again?" asks Donna. "If I'm lucky," says the Doctor. "You better come when I call you," says Martha, and the Doctor says he will. Not going with him right now doesn't mean a permanent separation; they're alive, and so is he, and though he never says so out loud, he really needs the prospect of seeing them again more than they need him.