The game is up
The original meaning was 'the game is over - all is lost'. More recently it has come to be used to mean ' we have seen through your tricks - your deceit is exposed'.
From Shakespeare's Cymbeline, 1611:
Euriphile, Thou wast their nurse; they took thee for their mother,
And every day do honour to her grave:
Myself, Belarius, that am Morgan call'd,
They take for natural father. The game is up.
See other phrases and sayings from Shakespeare.