Accompanied by , Bethany tells for the first time of the moment she watched the shocking footage of her dad's murder - and how she will not rest until she finds out where her father's last resting place is.
On the way, the 22-year-old is confronted by one woman of ISIS in a fraught and tense encounter and sees the spot where her father's executioner, Mohammed Emwazi - otherwise known as Jihadi John - is thought to have been killed in a drone strike.
David, originally from Holderness, East Yorkshire, had family links to Perth in Scotland.
He was a humanitarian worker who had gone to Yugoslavia in the aftermath of the Balkan Wars in the 1990s to help people rebuild their lives.
His mission in Syria was much the same but he was abducted in 2013 while working in an aid camp.
His execution was filmed and released as part of the warped ISIS propaganda footage.
More than six years later, Bethany carries with her a dossier detailing all the kidnappings of western hostages, to when the beheadings started - beheadings that would include her father.
"I think it brings me that one bit closer to solving the puzzle of where he is now, where the remains might be - and it just makes me feel like I'm doing something rather than sitting and relying on other people to do it for me," she says.
All four of the so-called "Beatles" - the group of British ISIS fighters given the moniker of the 1960s pop band because of their British accents - are included in her dossier.
"For me, this was more about trying to understand what could drive someone to do what they did ... and, although some of them had troubled backgrounds, it didn't really, it still doesn't add up to why someone would think it's acceptable to go join a terrorist organisation and behead a journalist and aid workers."
She says she - and others - still struggle to understand the motivation of these people to leave their homes, their families and carry out these barbaric acts when they've not been brought up that way.
Bethany has watched the video of her father's death. "I thought, enough is enough - I going to see if it's real," she said.
She locked herself in a bathroom and watched it.
"I thought I would be really upset but it was just numbness. I think it was shock, so for a while, I didn't feel anything.
"Then, a few hours later, the grief started to strike."
"I need to come to terms with it, and close that off and move on."
Bethany travels to a camp where thousands of people live and work, a camp similar to where he father would have worked.
Bethany describes how people are living there as "primal".
There she meets some of the women of ISIS.
One of them is a 25-year-old British woman, Tooba Gondal. She claims she was radicalised through Twitter but is also accused of recruiting other women.
Bethany shows her a picture from the video which shows her father's murder - she recognises 'Jihadi John'.
"I can only say my apologies to you and that I feel your sorrow," Gondal tells her.
"It's not just words, I honestly mean that. I cannot be held responsible in any way, I did not give my allegiance to this."
But another woman from Tunisia confronts her.
She says Daesh killed her husband and her brother, and not just Bethany's father.
The exchange gets heated as the woman says those in the camp are also paying a price.
Bethany is forced to walk away.
From the tension in the camp, Bethany is then taken to see the Kurdish fighters who, with support from the international community, did much to help break the back of ISIS resistance in northern Syria.
Bethany shows a photograph of her and her father to the SDF Commander, Mustafa Bali, and he says: “I mean, it’s really sad. I have a daughter of the same age.
“Even before I saw the picture I knew why you were here.
“For every body we find we will take samples of their DNA hoping that in the future we can find ways to identify them.
“We have made a decision that when we find a victim we will rename that area as a memorial to them.”
She heads to Raqqa - the former stronghold of the caliphate, now a city in ruins.
Commander Bali takes her to the spot where her father's killer met his own end, killed in an drone strike at the end of 2016.
Bethany recalls hearing the news of Emwazi's death: "When I got the news, I was ecstatic.
"I had a party and now, actually being here and seeing it, makes it more real.
"It does bring that sense of relief, that he's now finished with."
Nearby, an exhumation is underway. A mass grave has been discovered, containing, it's believed, the remains of as many as 30 bodies.
It brings some hope for Bethany that she, too, might one day find the remains of her father.
"There's always that hope, and that hope will never fade, even if it's another six years, 20 years, 30 years, I won't stop trying until he is found," she says.