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.
(..) , and we reviewed all the evidence to date. He was interested. Asked all the right questions. Then I showed him the film... taken from the museum's hidden monitoring cameras. This was the last group to go through the museum before it was robbed. You recognize any of these people? No. No. (..)1975 The Return of the Pink Panther