In the end, it is Sheldon who saves them.
"We told you aliens exist!" is the first thing that Howard says when Penny enters Sheldon and Leonard's apartment.
When the monster landed in San Francisco, the Cheescake Factory was packed full of people trying to get a glimpse of what was going on on their television sets. But then the true horror of the situation began to set in, along with the sinking realisation that they weren't that far from 'Frisco.
Within a half hour, the place was empty, and the staff soon followed the customers' lead. Most headed home, determined to pack and flee from California. Penny headed to her neighbours' apartment, and she thinks that that says a bit too much about her.
In the end, they watch the fiasco unfold in front of them together. It doesn't take long before Raj and Amy join her, Leonard, Howard and Bernadette, and the six of them watch in horror as their world suddenly turns into hell.
Howard never mentions those words to her again.
Sheldon misses nearly the entire thing, busy on his phone arguing with someone for nearly five days – he starts just minutes after Penny arrives, and doesn't stop until the chaos is nearly over.
When the creature – they're calling it a kaiju, they're calling it Trespasser – is finally dead and the world can breathe a sigh of relief once more, Sheldon tosses duffel bags to everyone in the apartment.
"You should all pack," he says. "We're moving."
It takes them some time to realise that he's not joking, and when they do, the questioning starts.
"Cambridge's been pestering me to come work for them for the last two months," he finally tells them. "Honestly, they're been rather troublesome, calling me while I'm busy thinking. But after this, I've decided to accept. And since I'm a genius, and genii scientists are soon going to be hard to find without engaging in a hiring war, they've agreed to let me bring by own team. That," he says, noticing their confused looks, "means you."
Of course, the questions don't stop there. But all that will say is, "Scientists are going to be fought over soon. Anyone with some sort of educational background is going to be necessary – indeed, I foresee the situation becoming so desperate that even Wolowitz might become a prized commodity."
In the end, none of them can refuse. They might not understand Sheldon, but working at Cambridge is a once in a lifetime opportunity that none of them would turn down.
So they all pack, and Sheldon takes it upon himself to make sure that their families follow them – at least, those of their families that care.
When Penny asks him why she's supposed to be moving, he just smirks at her and says that Cambridge was willing to anything to obtain his employment, even agree to sponsor her move to Britain. He tells her that she can be a waitress-cum-actress just as well in a different continent, and just like everyone else, she cannot argue.
They're talking about Britain, after all, Britain that's home to some of the best fashion and acting talent in the world. Really, it was never even going to be an argument.
It's only when they're at LAX, waiting for immigration, that Penny understands.
It's crowded, so crowded, with droves of men and women just waiting to get on a plane that will take them away. Away from it all, the madness and death and destruction, the constant reminders that all that they once knew is gone and can never come back.
It's easy for them, being sponsored by one of Britain's most prestigious universities. But she sees the desperation in the eyes of the people who are just waiting for a free seat on a plane, and she realises how lucky they all are.
Because even though none of them say it, the fear still lurks somewhere within them. What if Trespasser wasn't the only one? What if there will be more?
Two months have passed since the world was turned upside down, and Penny's changed her tune once again.
There haven't been any attacks, and the world has brushed it off as a one-off odd happening. Penny agrees with the majority, and so do everyone else – that is, apart from Sheldon.
Sheldon sneers at them every time they suggest that the world can take a breath once more, that they're safe. That there won't be any more kaiju appearing from the depths of the ocean to attack them.
They just chalk it up to Sheldon being paranoid again. Sure, his alien invasion fear almost came true, but the key there is almost. The kaiju came and gone, and even though Trespasser did overwhelming damage, there aren't going to any more coming through.
And so another four months pass.
Manila becomes headlines all over the world. Another one of them – they're calling this one Hundin, whatever that means – and suddenly they know that Trespasser wasn't the only one. It was never going to be the only one.
They – their world – are under attack, and the only way to kill the invaders is to doom themselves in the process.
After that, the second kaiju, the world prepares for war. Nuclear weapons are the only way to fight back, at least until something better is developed – and suddenly Penny realises just what Sheldon had meant months ago, when he said that the best scientists would be fought over fiercely – so countries the world over start to weaponise material previously only used for energy, or build entirely new nuclear programmes.
And as humans build, the kaiju come. More and more cities are turned into barren wastelands as the months pass, and land rates soar in cities that far away from the sea. A team of scientists – one which Sheldon, Leonard and Raj are part of – find out that the Breach from which the kaiju emerge is located in the Pacific Ocean near Hong Kong. It's projected that Europe is relatively safe from the kaiju, and suddenly there's an influx of refugees from all over the world.
Here, in Cambridge, they've found themselves a new home. They still gather round at Sheldon and Leonard's apartment as often as they can, but these days, the thing that's playing on the television is not one of the boys' strange shows that Penny's never understood, but the news channel.
After all, reality is odder than fantasy now.
So Penny sits and watches, and she knows. Had they still been in Pasadena, in the United States, there's a greater than average chance that they wouldn't still be alive.
In the end, it's really Sheldon who saves them all.
A/N: Yeah, so I have absolutely no idea what came over me with this one, but I'm actually pretty pleased with the results. I know that the atmosphere of the piece is much darker than BBT, but seeing as it's set in the Pacific Rim universe, I think it's justified.
I hope you guys liked it! Please don't forget to drop a review on your way out - this is my first time writing for BBT, and I'd love to hear what you guys thought about it :)