When NSA contractor Edward Snowden downloaded tens of thousands of top-secret documents from a highly secure government network, it led to the largest leak of classified information in history — and sparked a fierce debate over privacy, technology and democracy in the post-9/11 world.

Now, in United States of Secrets, FRONTLINE goes behind the headlines to reveal the dramatic inside story of how the U.S. government came to monitor and collect the communications of millions of people around the world—including ordinary Americans—and the lengths they went to trying to hide the massive surveillance program from the public.

In part one, a two-hour film premiering Tuesday, May 13 at a special time (9 p.m.), FRONTLINE went inside Washington and the National Security Agency, piecing together the secret history of the unprecedented surveillance program that began in the wake of September 11 and continues today – even after the revelations of its existence by Edward Snowden.

Now, in part two, premiering Tuesday, May 20 at 10 p.m., veteran FRONTLINE filmmaker Martin Smith (The Untouchables, To Catch a Trader) continues the story, exploring the secret relationship between Silicon Valley and the National Security Agency, and investigating how the government and tech companies have worked together to gather and warehouse your data.

Smith investigates the ways Silicon Valley has played a role in the NSA’s dragnet, and blurred the boundaries of privacy for us all.

“As big technology companies encouraged users to share more and more information about their lives, they created a trove of data that could be useful not simply to advertisers—but also to the government,” Smith says. “Privacy advocates have been worried about this since the early days of the Internet, and the Snowden revelations about the scope of government spying brought their fears into high relief.”

“If the FBI came to your door and demanded photos of your wedding, the names and daily habits of your children, the restaurants you frequent, who you’ve called and texted for the past month, and where you’ll be staying on your upcoming vacation, you’d call your lawyer,” Smith says. “But that’s exactly the sort of information we’re all sharing by living our lives digitally — and the government has taken notice in a big way.”