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.

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Read more about Walker's story here.

Ask your questions below and Walker will answer them from midday.