keep someone in the dark
keep (someone) in the dark (about something)
To keep someone uninformed (about something); to exclude someone from full knowledge or disclosure (of something). Keeping taxpayers in the dark about how their money is being spent is not how government should operate. I don't fully trust John to keep our plan a secret, so I think it best that we keep him in the dark for now.
keep someone in the darkor
leave someone in the dark
If you keep someone in the dark or leave someone in the dark, you do not tell them about something In many cases, the government itself was being kept in the dark about what was going on. She thought you shouldn't be left in the dark but should be told as soon as possible.
keep someone in the darkensure that someone remains in a state of ignorance about something.
2003 Village Voice It's payback time for an administration that…has ignored lawmakers and…deliberately kept them in the dark.
in the dark, to be/keep someone
To be mystified or uninformed; to fail to inform someone. The figurative use of dark for ignorance is very old indeed. “We can’t keep it dark any longer,” wrote the Roman playwright Plautus (Aulularia, ca. 210 b.c.), and Shakespeare wrote, “Till then I’ll keep him dark” (All’s Well That Ends Well, 4.1).