For most of the past decade, Silicon Valley has been booming. But in 2016, fear seeped into the market. Unicorns suddenly had to prove their worth. Companies that had raised hundreds of millions of dollars began quietly folding. Investors wondered whether a long-anticipated downturn had finally arrived. Yet even as some startups began to disappear, venture funds raised record amounts. What happened and what's next? We'll explore these questions and many more in our new series, "The Down Round."