Big tech muscles in: The 12 months that changed Silicon Valley forever

At 1 p.m. on a Friday shortly before Christmas last year, Kent Walker, Google's top lawyer, summoned four of his employees and ruined their weekend.

The group worked in SL1001, a bland building with a blue glass facade betraying no sign that dozens of lawyers inside were toiling to protect the interests of one of the world's most influential companies. For weeks they had been prepping for a meeting of powerful executives to discuss the safety of Google's products. The deck was done. But that afternoon Walker told his team the agenda had changed, and they would have to spend the next few days preparing new slides and graphs.

In fact, the entire agenda of the company had changed - all in the course of nine days. Sundar Pichai, Google's CEO, had decided to ready a slate of products based on artificial intelligence - immediately. He turned to Walker, the same lawyer he...