I first saw Radhika walking towards me on a lush green lawn at a refuge for trafficked women in Kathmandu. She struck me as someone beautiful and vulnerable in equal measures. Holding her young son Rohan tightly, she sat crossed-legged opposite me and began to tell a story so powerful, I knew I could and should never forget it. It was the beginning of a special relationship that exists to this day.

I had been sent to Nepal by The Sun in July 2009 to cover the story about Gurkha soldiers who wanted equal pension rights to their British colleagues. Along with 15 other journalists and the captivating actress and campaigner Joanna Lumley, I journeyed from the capital to Jhapa, Pokhara, Dharan and back again, witnessing first hand the overwhelming gratitude shown to Joanna following her much publicised UK campaign for Gurkha equality.

On the last day of our week-long trip, Joanna announced her intention to visit a Kathmandu shelter for trafficked women called Maiti Nepal, which translates as Mother’s Home. I asked if I could join her and was immediately moved by the work being done to rehabilitate women and children who had experienced horrific sex trafficking crimes.

I asked the shelter’s founder Anuradha Koirala if I could meet a girl who best summed up the experience of human trafficking, promising that I would do my best to get her story published to raise awareness. Anuradha rushed off and moments later Radhika and Rohan appeared. I sat spellbound for over two hours as her story spilled out.

Aged just 16, she was drugged by a trafficking gang who removed and sold her kidney before selling her into a series of Indian brothels. She was separated from her beloved son and forced to have sex with more than 20 men a day. But she refused to accept her lot and in a desperate bid to be reunited with her son, she fought against the odds and escaped, living to tell me the tale.

Afterwards, I returned to my hotel room and howled. It was rare to be so moved by a story after so many years in journalism but I knew that it was special and had to reach a greater audience.

I quickly found a publisher for Radhika’s Story after returning to London and the first edition of Radhika’s Story: Human Trafficking in the 21st Century was published in 2010. I’m proud to say that it has even reached the realms of the White House, receiving plaudits from Hillary Clinton. It remains in print and is being re-launched and updated by the German publisher Heyne this year.

I’m also delighted that Radhika has benefitted from the book’s royalties, which she is saving for her son’s future.