He's accused of having a 'hidden agenda'. [=a secret plan]
His suggestions have a 'hidden' [='secret'] purpose.
There was a 'hidden' flaw in the airplane's design.
(..) Please! Strange! You remind me of him a bit. It's here, in the castle. In the place where everything is hidden. If you have to ask... ... you will never know. If you know... ... you need only ask. Thank you! (..)2011 Harry Potter and the Deathly Hallows: Part 2
(..) ... Do you read? We've a new weather report. Lightning has struck. I repeat: Lightning has struck. What's the fun, Harry? Okay. There's something we need to find. Something hidden here, in the castle. And it may help us to defeat You-Know-Who. - Alright, what is it? - We don't know. - Where is it? (..)2011 Harry Potter and the Deathly Hallows: Part 2