◊ If you are in on something you have knowledge about it or are involved in it.知晓;参与
They were all in on the scheme.他们全都参与了那场阴谋。
The characters are convinced that they're on another planet, but the audience is in on the joke. [=the audience knows they are not on another planet]这些剧中人物坚信他们是在另一个星球上,但观众知道这只是个玩笑。
I let them in on our little secret. [=I told them our secret]我把我们的小秘密告诉了他们。