This is The Guardian.

Hey, it's Mike. Today we bring you the first four parts of an incredible story

about a woman who escaped modern slavery right here in the UK.

The Guardian's award-winning human rights journalist Annie Kelly reports.

And a warning before we start, this series includes references to

suicidal thoughts and descriptions of sexual exploitation and violence.

So please take care when listening.

On the sixth floor of a posh new bell blocker flats in Sumbrian Thames,

Martin, a detective at Surrey Police, is silently edging down a carb to corridor.

His team follow behind him pressed against the wall towards a closed apartment door.

It's just after lunchtime on a Friday in September 2019.

They've received a tip off from a sex buyer, but the flat is a brothel and that something isn't

right. There could be a woman inside who needs help.

Martin and his team are wearing protective stab vests.

They don't know what they're going to find on the other side of the door.

An undercover officer pretending to be a customer knocks on the door.

You can open up, look, come on, I haven't got long.

Just got comments like that.

They wait.

Hello?

Okay.

They can hear a woman's voice from inside the apartment, but she's not letting them in.

...