découvrir le pot aux roses

to uncover a hidden secret

Used when something people were trying to keep quiet finally comes out into the open.

Les enquêteurs ont fini par découvrir le pot aux roses.

The investigators finally got to the bottom of the whole scheme.

Dates back to the 13th century, when 'découvrir' meant to lift a lid. A 'pot aux roses' was a small box where well-off young women kept perfume and rouge, and it often hid love notes or other secrets underneath.