Cerebral was a buzzy Silicon Valley startup that set out to transform mental-health services in the U.S. In just a couple of years, the company attracted thousands of patients, raised hundreds of millions of dollars and partnered with star Olympic gymnast Simone Biles. But some people who worked at Cerebral say that, along the way, the company's focus on growth interfered with patient care. And now, Cerebral is under federal investigation. Cerebral says it provided high-quality care to thousands of patients who might not otherwise have had access.

In a new four-part series, WSJ's Rolfe Winkler and Khadeeja Safdar take us inside Cerebral. We'll meet some staff and patients who are part of Cerebral’s story, and explore the company's origins and explosive growth, as well as the consequences of that growth.