During the summer of 2012, Karen and Rick and Kyle, their 23-year-old son, took to the road with Erika’s Saint Bernard and traveled more than 5,000 miles in the national parks of America. It was Karen’s idea to try to deal with the family grief by means of long hikes in the redwoods. Pulling into a small town in Oregon, she noticed a paperback copy of a book by Dean Koontz on a rack in a small grocery store. The novel spoke so directly to her that she wrote a long letter to the author, explaining how moved she had been by it and what had happened to her daughter. Koontz promptly responded. “I receive much fine mail from readers,” he wrote, “but none more moving than your lovely and exceptional letter.” Koontz explained how the wife of someone close to him had suffered two strokes. She too was on NuvaRing.

In my last conversation with Megan Henry, she mentioned that she was almost back to normal and was training again. She will have a much higher risk of blood clots for the rest of her life, she said, and if she gets pregnant she will likely have to go on a painful regimen of injections of Lovenox to prevent clots. She will never be allowed to use any kind of hormone therapy.

In the initial response to my e-mails and phone calls requesting an interview with Merck chairman Ken Frazier or one of the company lawyers, a pleasant Merck employee named Lainie Keller asked how the company could be helpful. When I explained that I was focusing only on NuvaRing, she said she understood magazine deadlines and would get back to me soon. Two days later, I received an e-mail from her. “Ken Frazier and our other colleagues are not available to participate in this opportunity,” she wrote, and she directed me to several Web sites, including ACOG’s and Merck’s, “to help provide perspective.” At the end of the e-mail, Keller included Merck’s official statement: “Blood clots have long been known as a risk associated with combined hormonal contraceptives. The FDA-approved patient information and physician package labeling for NuvaRing include this information. . . . We remain confident in the safety and efficacy profile of NuvaRing—which is supported by extensive scientific research—and we will continue to always act in the best interest of patients.”

All this summer and fall, the wrangling went on behind the scenes over the Lidegaard study of NuvaRing. Early in October, as Denton combed the Internet for developments, he got an alert that the F.D.A. had approved changes to the NuvaRing label. Merck had included certain results from the Kaiser study and Merck’s own study but had not included the Lidegaard study. On his way to Ibiza for a long-delayed vacation, Shkolnik struggled to make sense of this. Soon after he landed, he learned that Merck Canada had indeed already changed its label and included the warnings from Lidegaard. That was, for the plaintiffs’ team, enough to indicate that the F.D.A. had given in to what seemed like pressure from the American drug companies. But for the warriors of mass tort, the newest development was significant. The lack of a stricter warning could extend the battle. In fact, the Merck Canada decision might ironically turn out to be a plaintiff’s lawyer’s dream. Shkolnik could hardly wait to get all that into an argument.

Thousands of cases are now being settled on behalf of plaintiffs who say they were stricken with clots after using Yaz or Yasmin. In the United States, more than 13,000 cases were filed against Bayer. There have been at least 100 alleged deaths. The F.D.A. came down hard on Bayer. “These sorts of stories usually appear in the business section,” the mother of a 31-year-old Sony executive who had died in childbirth, allegedly of complications from having taken Yaz, wrote me during my research. “They never seem to have a ‘face.’ The real face is very beautiful, only 31, highly accomplished, and will never age.”