One's plan or scheme has been discovered and/or thwarted; one's game, trick, or deception is at an end. A variant of the much more common phrase "the jig is up." Your jig is up, Senator Marten! Your tax evasion has been found out, and the police are here to escort you to prison. We were going to play a practical joke on David, but when he noticed our car parked out front, I knew that our jig was up.

The plan or scheme has been discovered and/or thwarted; the game, trick, or deception is at an end. The jig is up, Smith! The police found your fingerprints all over the safe. We tried to smuggle a kitten into the house, but when mom saw me carrying a saucer of milk, I knew that the jig was up.