The man the intelligent, beautiful middle-class Sydneysider had fallen in love with had become her captor, pimp, tormentor and terrorist.
"He pressed the hot knife up against my throat and I felt like he was going to slit my throat so I jumped up and he just threw me back down and he kept strangling me and eventually I was just screaming," Lang tells Tara Brown in a simultaneously confronting and astounding 60 Minutes interview to air on Sunday.
On the surface, Lang's story almost defies belief. It's hard to digest, hard to watch. And it's even harder to look away from.
Meeting the charismatic Bastion in a Gold Coast nightclub was the start of a five-year nightmare which crossed continents and saw her forced into becoming a sex slave and stripper, trafficked around the world at the hands of the man who became the monster who beat her, raped her, and controlled her.
By the time she realised she had to leave, she couldn't. Instead she married him. And lied to her family about the hold he had on her.
"Once the violence started I couldn't see a way out. I was so fearful of him not only hurting me but also hurting my family," Lang says, chronicling the way Bastion lured her in, from the initial rush of romance to the first, brutal blows to her stomach which left her bruised and broken.
Many more beatings were to follow.
"He very much enjoyed beating me up and then having sex," Lang says.
"I let go of myself and my soul and let him control me."
But as brutal as Lang's experience is, Brown says the story is also one of strength - Lang's escape, finding the courage to talk to police, and ultimately testify in court as the main witness in an international case that saw the monster come unstuck.
"It was a very confronting story to hear because Katie just doesn't present as someone who could end up in such a vulnerable position," says Brown.
"She's got it all together - she seems to - she's well educated, she's articulate, she seems very confident in herself, and yet her experience shows how any of us could be vulnerable to someone whose aim it is to manipulate and trick you and then terrorise and terrify you into doing something that you don't want do."
The term for the state Lang ended up in - in fear if she stayed she would die, but too scared to leave, is Stockholm syndrome, and it's the first time Brown has seen it first-hand.
"Dr Frank Ochberg, the world's leading authority on Stockholm syndrome, describes the man Katie came into contact with as 'charismatic evil' - and nothing prepares you for that," Brown says.
"He makes the point there is no flaw in her - in fact, quite the opposite - she's incredibly strong and incredibly smart - but when you come up against someone like Baston, nothing prepares you for that.
"That trauma bond that is formed in some cases is a really confounding attachment, which can mean even if people have an opportunity to walk away, they choose not to.
"Actually choice is probably the wrong word, because that attachment has become so strong and is so contorted that choice really isn't part of it.
"It's not that they are so much physically retrained - far greater is they are psychologically enslaved, and that certainly seemed to be the case with Katie.
"I have seen that trauma bond in cases of domestic violence, but what made Katie's story different was the elements of the work she was made to do."
In September last year, a jury took just six hours to find Baston guilty of 21 charges, including sex trafficking through means of force, fraud and coercion and the importation of an alien for prostitution.
He was sentenced to 27 years jail in a Florida prison.
Lang, whose nightmare with Baston saw her forced into prostitution on the Gold Coast, in Dubai and in several states in the United States, was one of the main witnesses at the trial.