have a card/trick up your sleeve
to have an advantage that other people do not know about. I still had a card up my sleeve in the form of a letter from his father.
have an ace up your sleeve
to have an advantage that other people do not know about.
The new game show has an ace up its sleeve. It will allow viewers to play from home and win prizes.
have something up your sleeve
to have a secret idea or plan. If this trip doesn't work out I've still got a few ideas up my sleeve.