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 Mr. 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 chief executive, had decided to ready a slate of products based on artificial intelligence — immediately. He turned to Mr. Walker, the same lawyer he was trusting to defend the company in a profit-threatening antitrust case in Washington, D.C. Mr. Walker knew he would need to persuade the Advanced Technology Review Council, as Google called the group of executives, to throw off their customary caution and do as they were told.

It was an edict, and edicts didn’t happen very often at Google. But Google was staring at a real crisis. Its business model was potentially at risk.