the lowdown on

low-down

1. adjective (used prenominally) Dishonest or unfair; vile or despicable; contemptible. The guy I've been seeing turned out to be a low-down, cheating rat! You're nothing but a low-down coward, you know that? My low-down boss fired me, even though it was his mistake that lost us the client!
2. noun The truth, facts, or most pertinent information about something. OK, here's the low-down: I've got a great business opportunity lined up, but I need to borrow a few thousand dollars to get it off the ground. This is Jane—she'll give you the low-down on day-to-day tasks around the office.

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]
See also: lowdown, on