show (one's) cards
To make one's plans, intentions, ideas, or resources known to others, especially those previously hidden or kept secret. (A variant of "show one's hand"; both phrases refer to displaying the cards one has in one's hand during a card game.) In business negotiations, it's important that you don't show your cards right away, or you might risk losing out on the best deal possible. Pressure from the IRS is forcing the notoriously secretive CEO to show his cards regarding his company's tax profile and offshore accounts.