Wearing just their underwear, the girls line up with their backs to the wall, arms by their side, heads down, frozen to the spot. They dare not move.

Their captors walk up and down the line – picking them seemingly at random and tapping them on the shoulder – ‘You, you, you and you… come with me’.

In the back of a warehouse truck, they are driven for miles across the scorching Nevada desert until they reach a hotel. There, they are forced to have sex with up to 25 men one after the other.

This was life for Korean-born American Chong Kim who, at 19 years old, was sold as a domestic sex slave in 1994 to Russian gangsters and held captive for more than two years.

“The clients never came to the warehouse,” she recalled “That was just where we slept. There was nothing there but bed mats…