Every night in Sonagacchi, Kolkata, more than 10,000 women stand in line waiting to be picked up for sex. Many of them were trafficked into prostitution.

But now Freeset, a Christian business, is in the process of buying a building that has the potential to transform India's most infamous sex district. The 20,000 square feet Gateway building  is situated right at the front door of the red light district. The new space will give Freeset the opportunity to employ more women, and will house other new businesses that are able to free women from sexual slavery.

"The Gateway building is really exciting," says Kerry Hilton, founder of Freeset. "We don't want that building to be turned into more brothels, where they could probably have 1,000 women working. We're keen to turn that right around and say instead of more women, more opportunities for the kind of jobs that set women free."

Freeset began in 2001 by offering 20 women in Sonagacchi alternative employment making bags. Today more than 160 women work there, and Freeset is not alone. There are many other Christian businesses working in Sonagacchi – businesses like Sari Bari and Love Calcutta Arts – and together they have made the decision to try to purchase the Gateway building. These businesses have a shared vision to give women working in Kolkata's sex trade the choice to leave an industry many of them never chose to enter.

"We have the most incredible relationships with each other," Kerry says. "There's no understanding of competition. We help each other when there's crisis – and there's crisis all the time in our neighbourhood. When it comes to Christian community, it's the best model I've ever seen."

One of the biggest issues facing those who want to start businesses in Sonagacchi is a lack of space. The Gateway building is huge, so as well as housing an expansion of Freeset's current bag and t-shirt business, Kerry says that start-up businesses could come and work out of it for three years. The building would act as a business incubator, gradually helping more and more freedom businesses to start and so providing an increasing number of opportunities for Sonagacchi's women.

But Kerry and his wife Annie have received death threats for their work in the red light district over the past 15 years and the expansion of Christian business in Sonagacchi is unlikely to come without a fight. There are those who don't want to see businesses that free women from prostitution succeed – those profiting from the human misery in Sonagacchi. "I would love to say we'll buy the building and everyone will be extremely happy," Kerry says. "But if the freedom business grows, the business that seeks to exploit women suffers."

Despite this, Freeset has signed an agreement with the Gateway building. But they still have a long way to go. "It's a wonderful opportunity – and yes, we have got to find $2.5 million to complete the deal by June," says Kerry. "But we have a big God."

The Christian business community in Sonagacchi is providing freedom for women who have horrific stories to tell. Women like Pavitra (not her real name).

Pavitra is the youngest of 10 children and never had the chance to go to school. She was married at 13 and separated a few months later, after being severely neglected by her husband and his family. At 15, Pavitra accepted a job in a neighbouring village. She was trafficked to Kolkata and sold into prostitution.

"After I had my first customer, I cried all day," Pavitra says. She asked to leave, but was told that she was a 'bad woman' now and could never go home.

Two years after arriving in Sonagacchi, Pavitra managed to escape the red light district with a 70-year-old customer who told her he would help her. But instead, he beat her, cut her face and arms, stole all of her jewellery and then left her. She had nothing, and felt she had no choice but to return to prostitution. She started drinking alcohol to numb the pain.

Pavitra was one of the first women to be employed at Freeset, after years of working in prostitution.

"I've found great love," she says. "I have moved from a journey of darkness to a journey of light. Now my heart is burning for the women who are like me. I know that it is in God's heart that these women find freedom."

Pavitra knows better than anyone the huge challenges facing women who want to leave prostitution. She speaks of one Nepali lady who doesn't want to work in the sex trade any more. In order to get out, this woman will have to pay her madam back the amount she was 'purchased' for – money it will take her a lifetime to earn.

Freeset doesn't only work to give women another way to earn a living, it also provides counselling, healthcare, childcare, budgeting skills and help with debt management. With more Christian businesses working out of the Gateway building, which anyone entering or exiting the red light district will have to pass, more women will be able to come and seek help. The ground floor will be entirely dedicated to helping women work through the complex issues they are facing – whether or not they choose to leave prostitution.

Kerry says that he and Annie will carry on working to bring freedom to Sonagacchi's women for the rest of their lives. "You get a chance to invest in freedom. You get a chance to invest in a woman that is exploited and finds herself raped and abused every night – and she gets to be free and understand that there is a God who loves her," he says. "Find me a better investment than that."

● If you wish you could do something practical to help the thousands of women trapped in prostitution in Kolkata, maybe you can. Visit www.freesetgateway.com to find out more about the Gateway building and what you can do to help. There are many ways UK Christians can support Kolkata's freedom businesses and the women working in them. You could buy fair trade gifts from Global Seesaw, the UK distributor of products produced by Freeset and other Christian businesses in Sonagacchi. Or you could also host a freedom party, selling fairly traded products to your friends or at your church or small group.

Sarah Stone is a copy writer at a British Christian mission agency.