be kept in the dark (about something)

To be kept uninformed (about something); to be excluded from full knowledge or disclosure (of something). The president was kept in the dark about the CIA's assassination attempt so that if things went sour and came to public light, she could claim plausible deniability. I don't fully trust John to keep our plan a secret, so I think it best that he be kept in the dark for now. Somehow, everyone knew that Alicia had quit school except for me—I was totally kept in the dark.