let in on

• • 让…参与；与…共享：

    His classmate refused to let him in on their extra-curricular activities.

    他的同班同学不让他参加他们的课外活动。

  • 让…知道(秘密)；告知：

    I'll let you in on our plans after dinner.

    饭后我会让你知道我们的计划。