under wraps
under wraps {adv.} or {adj. phr.}
Not allowed to be seen until the right time; not allowed to act or speak freely; in secrecy; hidden. — Usually used with "keep".
We have a new player, hut we are keeping him under wraps until the game.
What the President is planning will be kept under wraps until tomorrow.
The spy was kept under wraps and not allowed to talk to newspapermen.
Compare: UNDER COVER.
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Source: A Dictionary of American Idioms