This week for our "What I do" series, we'll be speaking to undercover investigator Daniel Walker.
The former detective took a job in 2002 with a private US organisation that infiltrates brothels suspected of coercing children into prostitution.
Over the next four years Walker's undercover work helped save hundreds of children - some as young as five - from being forced to work in brothels.
However his mission ended in a mistake that cost him his marriage and made him question his identity.
Read more about Walker's story here.
