I am driving myself mad with this. Google keeps offering the same few titles but it isn't any of them.
It was on in the last 10 years and was a uk mini series, set in a city like London.
I can't recall many of the details but there was a particular scene in the last episode I think, where there were some women who were being held captive, in a secret room in a large house. The police were searching the house and the girls were screaming and trying to attract attention, but the secret room had been soundproofed. As the police left the house and were walking back to their car, the female detective realised something and they went back in the house and rescued the girls.
I recall that it was a thriller type series and that I really liked it so hoping someone else recalls it.
It wasn't Thirteen, Hidden, The Captive or The Missing.