I'm a fastidious road-crosser. But, engrossed in conversation with someone as interesting as Yeonmi Park, how was I supposed to spot that double-decker?
As the red behemoth rounded the corner, tearing through puddles, Park squealed. I instinctively gripped her arm and flung us both backwards. She let out an uneasy laugh. "I only just arrived in England," she said. "I don't want to die here."
We were en route from the Houses of Parliament to an Italian restaurant favoured by Westminster's pasta fans. Park had just addressed the All-Party Parliamentary Group on North Korea - a committee dedicated to raising awareness of humanitarian and security issues inside the cryptic state.
London was just one stop on a tour that saw Park attend the One Young World Summit in Dublin - where she appeared alongside Sir Bob Geldof and Kofi Anan - and addressing a TEDxYouth event in Bath. Between engagements she's given talks and interviews and has met with a major publishing house about a book deal.
It's no wonder - Park is blessed with a rare gift: remaining convinced of humanity's goodness despite witnessing its worst atrocities. Back in North Korea, her father had been a mid-ranking civil servant with a sideline in sales of gold, silver and nickel. In those days, any trading was a serious crime, and Park's father was imprisoned and tortured. After bribing his way out of prison her family escaped in 2007.
"I'm extremely grateful I was born in North Korea," she told me. "If that didn't happen, there's no way I could understand other people's pain. I couldn't understand being scared or [being] raped."
Park was referring to a moment when, separated from her father, her mother was raped in front of her by a people smuggler who had threatened to turn them into the Chinese authorities unless he could have sex with the 13-year-old Park. Desperate to protect her daughter, her mother offered herself instead.
"If caught by the Chinese authorities, North Korean refugees face deportation," Park explained. Once returned to North Korea, escapees face torture, imprisonment and death. Any returnee who is pregnant is forced to have an abortion in case the child is mixed race, such is the racist ideology of the Kim regime. "The biggest thing Western governments can do to help is to pressurise China to end its extradition treaty with North Korea and allow escapees full refugee status," she continued. "This will end the rape and abuse of refugees."§
Despite having a strong accent, Park communicates with clarity. Her fight for justice and equality makes the air around her seem lighter. It made the tough questions I had prepared about the duplicitous nature of her fast ascent to fame seem cynical. It seems almost impossible, too, that she's never had any media training.
"Lots of people think that [my high profile] is benefiting me, but I'm risking my life," she says. "The South Korean government doesn't want me to [speak out]; they say: 'You must stop because we cannot protect you if you continue,' and that is true. The North Korean government are out to get me.
"I can't say if I enjoy the attention or not," she continued. "It's really exhausting. But every speech and every interview is extremely important to me because it could be my last one. Every night I think, 'If someone killed me, then what is the most important message I can give to humanity?'"
Remembering a comment she made at the Parliament session about North Koreans living in the South committing suicide at a rate three times higher than the national average, I wonder how she survived the despair that killed so many others.
The North Korean government are out to get me
"There's no difference between me and suicides," she replied quickly.
But there is, obviously: you're alive and they're not.
She paused and then blurted out: "I attempted suicide twice. I ate lots of medicine, but luckily my mum saved me." She started speaking faster. "And you know what? Those moments taught me a lesson, that life is a gift, no matter how hard it is. Who knows what will happen? Who knew I would come to London? That is a dream come true for me."
For a long time people thought that change wasn't possible in North Korea. But, as Park told me earlier this year, the invisible walls around North Korea are being knocked down, thanks to the influx of foreign books, films and music. The regime can't seem to stem the flow, despite heavy crackdowns.
"Reading Animal Farmset me free from the dictatorship in my head," said Park. "I could see all the tactics used by the regime to control us - they were all in that book. Until then I thought everything that wasn't part of the regime was evil."
On any given day in North Korea, bales of DVDs are smuggled in, covertly tuned radios pick up the BBC World Service and USB sticks full of South Korean soap operas float over the border attached to balloons. "People think that change is impossible in North Korea," said Yeonmi. "But foreign media is setting us free."
As well as using foreign media to educate and inform, Park supports targeted sanctions that put the screws on the leadership, as long as measures are put in place to make sure the people on the ground don't suffer. "Western governments need to give money to the North Korean refugees living in Seoul who can distribute it to family members living back home - this way we can [ensure the safety] of the people on a grassroots level while putting sanctions on the regime."
Park's intelligence means she doesn't only campaign against the regime that tortured her family, but also gives considered solutions. In the last six months she has been featured in countless media outlets, from NBC to the Guardian. Wikitree currently pegs her Twitter exposure at 226,852. "I'm very lucky that people are listening to me," she says. "There have been plenty of voices raised before me, but they didn't get this big attention."
Of course, there are those who have pointed out that not many defectors are as young or attractive as her. "Why do I have to be pretty to talk about human rights?" Park says fiercely. She's right, of course. "What I am talking about is something very serious, but, of course, I know everything has pros and cons. If [the TV shows] want to use my appearance then I will let them because it is for a good cause." She's determined not to waste her sudden exposure, and recent speeches made at the Freedom Forum in Oslo and One Young World will only serve to further to her reputation as one of the planet's brightest young activists.
With no PR, Park manages her intensive media schedule on her own. But she is aided by friends, people like Charlotte Calkin, curator of TEDxYouth in Bath, whose Seoul-based daughter is her English teacher. Calkin accompanied us to dinner and, after the bus incident, Park clung to her arm like a child, seeming small in the din of the city.