By Max Godnick

Ever since Watergate, investigative journalists have been urged to "follow the money" to find the truth in politics. But how do you locate the funds that come from undisclosed donors?

"Dark Money" is a new documentary that aims to answer that very question. The film makes its national broadcast debut on PBS on Monday night, shining a detective's flashlight on mysterious corporate spending in politics.

"As a filmmaker, it was just a good mystery novel sort of spy thriller story that I knew we'd be able to tell," the film's director/producer Kimberly Reed told Cheddar on Monday.

The documentary extrapolates from a particular situation in Montana to explore a larger, more national problem in U.S. politics. Reed spends most of "Dark Money" tracking local journalist John S. Adams's attempt to uncover the truth about the funding behind her home state's tangled elections.

"I could see the storm brewing," Reed said. "It's a really good case study, because we can actually connect all of the dots."

Reed described "dark money" as any funding that "makes its way into an election, and you don't know where it's coming from."

Those contributions have been legally permitted ever since the 2010 landmark U.S. Supreme Court decision on Citizens United v. FEC, which established campaign spending as a form of First Amendment-protected political speech.

"That's just a recipe for corruption," Reed said. "I just think that our democracy was founded with the assumption that we're going to know who's trying to influence our politics."

She pointed to the hyper-centralization of dark money groups as the part of the problem that scares her most acutely. The unidentified financing stems from a small handful of groups, with just 15 organizations accounting for all dark money spending since 2010. The largest is Crossroads GPS, led by Bush-era political operative Karl Rove. The organization has since changed its name but still acts as the same entity.

Reed noted that the issue is non-partisan, with equal-opportunity offenders hailing from both sides of the aisle. But she did add that conservatives were the first to "weaponize" the funding tactic ー and the left has led the charge in finding legislative solutions.

With just weeks to go before the midterm elections, Reed cautioned voters and watchdogs alike to be mindful of this less-salacious corner of corruption and scandal ー the funding without high-profile names attached.

"Where we see big anonymous money going into elections, that's where we need to pay attention, especially if there's foreign influence behind it," she said.

For full interview click here.