in the dark about (something)

Uninformed about something; 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 about it for now. Excuse me, but why was I left in the dark about Alicia quitting school? This is a big deal!