in on, be

be in on (something)

To be participating or involved in something, often something secret or exclusive. The conspiracy ran deep, and several members of the administration were in on it. Wow, that really was a surprise. Were you in on planning this?
See also: on
Farlex Dictionary of Idioms.

in on, be

Also, get in on. Be or become a participant; be or become one of a group who have information. For example, Is she in on our secret? or I'd like to get in on this venture. [c. 1920] Also see barge in on; ground floor (get in on the); in good with.
The American Heritage® Dictionary of Idioms by Christine Ammer.
See also:
  • (you've) got to get up pretty early in the morning to (do something)
  • a/the feel of (something)
  • (I) wouldn't (do something) if I were you
  • a straw will show which way the wind blows
  • a crack at (someone or something)
  • all right
  • (you) wanna make something of it?
  • all for the best
  • a thing of the past
  • a slew of (something)