the lowdown on
The whole truth about something, as in We're waiting to hear the lowdown on what happened after we left. This term uses lowdown in the sense of “the basic or fundamental part.” [Slang; early 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.