have a card up (one's) sleeve(redirected from have a card up their sleeves)
have a card up (one's) sleeve
To have a secret plan, idea, or advantage that can be utilized if and when it is required. A reference to cheating at a card game by hiding a favorable card up one's sleeve. She has a card up her sleeve if they ever try to fire her, since she knows about the boss's unscrupulous business practices.