"Lovelace!" Babbage cries into the receiver. "Lovelace! Come here! I need you!"
Lovelace doesn't respond. Probably all tangled up in some nonsense with the Royal Wing, trying to make it apply to the latest developments out of Germany in Gauss' ridiculous games with -- although... He yanks himself out of mathematical reverie before he can fall off the side of the Engine. "Lovelace!" he bellows. "Now come on, algebraic consistency can wait! ... Oh, hullo."
She's standing behind and a hundred feet below him, looking up at him with an expression that could as easily be 'curiosity' or 'apathy' but is at least not one of her many and subtle variants in the 'loathing' family. "I was working on our accounts," she says.
That is sobering news, but he climbs down to better beam at her anyway. "Lady Ada von Lovelace--"
"That is not my title--"
"Lady Ada du von Countess Baron the Queen of Lovelace," Babbage continues, because what is he supposed to do, remember all her different forms of address? That would take up areas of his brain that could easily be used for brilliant calculations, "we are facing a terrible crisis."
She moves an eyebrow. That's probably 'interest' or 'nausea.' "Well, quickly, Babbage."
"It is about Christmas," Babbage says.
Lovelace's face darkens to unmistakable 'ire.'
"I don't see why you're so blasted insistent on avoiding it," Babbage calls into the receiver. "Christmas happens to us all once a year, like taxation and French revolutions and your annual decision to speculate on the applicability of Jacquard weaving to horse-racing and lose us a hundred crowns! Fine!" he adds, thumping a wrench down. "I shan't give you your--"
"It's broken!" Isambard Kingdom Brunel says, slamming the door open, and Babbage falls off his scaffolding entirely.
Several minutes later, when he has regained consciousness, he blinks up at Brunel, who is looking down with him with a combination of irritation and curiosity, perhaps to see if medicine is within the realm of his many talents. "Are you done?" he demands. "Because it broke."
"What broke?" This is Lovelace, from the stairs. Babbage cranes his neck to see that she is carrying her favorite wrench in her trouser pocket, which is straining uncomfortably at the load.
"PARLIAMENT," Brunel announces. "I HAVE BROKEN PARLIAMENT."
He means the building, it turns out. Not the system of government. That was broken before Brunel's efforts, a tangent upon which Lovelace objects to him going in the strongest terms. Brunel separates them with one sinewy bicep. "SILENCE," he says. He has evidently broken whatever usually modulates his voice out of capitals in the explosion as well. "WE HAVE ARRIVED."
They climb out of the carriage to see that the beautiful system of pneumatic tubes on wires, running straight and sure from St. Paul's to the fair ends of London, one of his best ideas, has totally collapsed. Babbage clutches his heart. "You blackguard! What could possibly have--"
Brunel points wordlessly at the cross at the apex of St. Paul's, which seems to be obscured by something--
"Ah," says Babbage, weakly. "I can explain."
Lovelace glares at him. "We agreed we were not going to implement the whirring saw emergency communication severance system until we were perfectly sure that it would only act in case of emergencies! You told me you had dismantled all the blades!"
"Well, when I say dismantled, I of course meant, ah, you see, but it seemed so beautiful in its original--" Babbage shakes himself off. "But this isn't what you called us out here to see!"
"THE EMERGENCY," Brunel bellows, gesturing to their left.
"Is that the American president?" Lovelace says, shading her eyes against the flames of the explosions. "But where did he get the giant metal spider chassis?"
"YOU SEE WHAT I MEAN ABOUT THE EMERGENCY."
"Your majesty!" Babbage puffs, running after the Queen, who is sweeping down the hallway with tremendous dignity and rage. "If you would just follow me to safet--" He is forced to stop. There is a faint sound that rises over the screams and crashes, a soft but determined voice butchering some dreadful song in a public street. Babbage hasn't very nearly been commissioned by the Queen to fight crime for nothing. He turns and leaps down the hall, passing Lovelace coming up it, and sprints out the door through the feet of President Andrew Jackson's Manifest Spider (Brunel Industries, Incorporated) to find the little wretch who is serenading them all.
"Stop singing about jangle bells this instant!" he demands, shaking the child only a little bit. "Can't you see that you're ruining Christmas? And my temper. If you insist on being a public nuisance-- I don't care in the slightest about your sleigh, one horse or otherwise!"
The child whimpers, but is silent, and in this blessed peace punctuated by the creaking from Westminster, he can hear Lovelace shout, "BABBAGE!"
"Oh no!" he cries, dropping the child. "You've broken Christmas and Lovelace's lowercase letters!"
"dv/dt," Lovelace greets him, and Babbage, still huffing from the climb up to the roof, manages, "ρcVp/2." Brunel ignores them both, packing more explosions into some small device than is necessary or, indeed, really physically possible. Babbage's fingers begin to fly over the punchcards as he sees what she's getting at. The experimental engine sends out massive amounts of steam and nearly bakes his fingers as he shoves the cards in one by one, and the output emerges--
"F=ma," Lovelace declares with finality, stands up, takes the device from Brunel, and shotputs it neatly into Mr. Jackson's third giant metal knee joint.
There is a satisfying collapse.
Exhausted, Babbage takes Lovelace's proffered lacy handkerchief. "This is what Christmas is all about," he opines, as Queen Victoria arrives in the wreckage of the chassis to deliver the most withering glare which Mr. Jackson has probably ever received. Even from the top of the building, they can feel the heat. "Miracles, the magic of cooperation, England's inevitable victory, punchcards."
"We will have to rebuild Parliament," says Brunel, his eyes lighting with lust. "I see a massive clockwork tower, three times the size of any structure in London! We will harness the power of time itself!"
"You have already built the Difference Engine to be three times the size of any structure in London," Lovelace points out, looking 'worried' or, perhaps, 'tired.' "Do you think this will mean war?"
"Oh, no, no, no!" Babbage says, distracted, as the engine tries to eat his fingers. "They do this every year. Which reminds me." He tugs his fingers free and pulls out her present from his waistcoat. "Here."
Lovelace takes the present gingerly, as though it might explode (which, conceivably, it might) and tugs open the ribbon to reveal his ingenious box. She touches one side of it. It hisses open in a gout of steam.
Eventually she says, "You bought me trousers."
"But not just any trousers!" Babbage says, puffing his chest out. "These are made of denim. Some Californian's idea, apparently, to deal with the masses of gold you have to carry around, you know. They are all the rage." He stops to peer at her. She is making an expression he can't identify at all. He adds, hopefully, "Besides, the pockets are triple-reinforced."
She holds them up to herself. They look like they might fit. "Happy Christmas," she says, clearly unsure if her output matches her input.
Behind them Brunel lets out a cry of masculinity and creative energy -- it shall be called Big Ben! -- and Babbage beams at her, clapping his hands. "Now!" he says. "Brunel clearly has this all under control. Let us go and dine on figgy pudding."