let in on

Related to let in on: in the wrong, pay a visit, ahead of schedule, stop short of, so much for

let (one) in on (something)

1. To give one information that is private or not widely known. All right, I'll let you in on what’s really going on here—we're planning a surprise party for Carla. The boss let me in on his plans for expanding the business.
2. To include one in something, especially that to which access is secret or privileged. I've been trying to get Martha to let me in on the deal she's striking with the Ferrelli brothers. Tom's been letting us in on the special offer he gets through work.
See also: let, on
Farlex Dictionary of Idioms.

let in on

Allow someone to know about or participate in something, as in I'm going to let you in on a little secret. This idiom was first recorded in 1904.
See also: let, on
The American Heritage® Dictionary of Idioms by Christine Ammer.

let (someone) in on

1. To reveal (a secret) to someone: They finally let me in on their plans.
2. To allow someone to participate in (something).
See also: let, on
American Heritage® Dictionary of the English Language, Fifth Edition.
See also:
  • go with bells on
  • give (one) a shot at (someone or something)
  • I'll get right on (something)
  • I'll get right on it
  • I'll see you (later)
  • I'll see you later
  • if not
  • I'll see ya (later)
  • in some neck of the woods
  • in this/that neck of the woods