About a month after news about the check-cashing broke came another bombshell. Arndt would be charged with four counts of statutory child rape and one count each of indecent assault and battery, drugging a person for sexual intercourse, contributing to the delinquency of a child, and possession of the drugs ketamine hydrochloride ("Special K") and methamphetamine. Middlesex County prosecutors allege that on September 5, Arndt was driving through Central Square in Cambridge and stopped to invite two boys, ages fifteen and fourteen, into his car to get high. Then, they allege, after dropping off the fourteen-year-old, he had sex in his car with the fifteen-year-old. The boys waited four days before contacting police. They said that Arndt had given them his cell phone number and told them his name was David. According to court records, when police dialed the number, Arndt answered, and he later admitted to having the boys in his car but said he had no physical contact aside from brushing one of the boys on the shoulder.

Soon after came Arndt's "poverty motion," asking the court to pay his costs because, according to his lawyer, he was indigent and his parents needed to save for their retirement. (His parents disputed the lawyer's account; he is now gone, and their lawyer, Stephen Delinsky of Eckert Seamans, is representing their son.)

Then, in August 2003, almost a year to the day after he first made headlines, Arndt made a splash again. He was arrested on August 8 and charged with possession of methamphetamine with intent to distribute. According to the postal inspector's report and other court records, on the morning of August 7, Arndt reserved a room at the Chandler Inn in Boston's South End for that night and asked that a party by the name of Frank Castro be added to his reservation. He also asked if any packages for him or his guest had arrived. Around 8:30 p.m.,Arndt checked in to Room 501 but apparently didn't stay there that night. Around 1:30 p.m. the next day, Arndt appeared at the front desk. Told that a package had arrived for Room 501 but that it was not in his name, Arndt signed for it and took possession of it. What he didn't know was that, the day before, postal inspectors in Los Angeles had found the six-pound Express Mail package addressed to Frank Castro in care of the Chandler Inn suspicious enough to get a federal warrant. Inside the box, they found a large, pink penis-shaped pinata. Inside the pinata, they found about two pounds of a white crystalline substance that tested positive for methamphetamine. That discovery led to a sting operation at the Chandler Inn, which in turn led to Arndt standing in Room 501, sweating profusely, trying to explain himself to a postal inspector.

The postal inspector reported that Arndt told him he had met Frank Castro online a few months earlier. When authorities went to Arndt's apartment in the South End, a man identifying himself as Alfredo Fuentes told them he and Arndt used to be partners but were now just roommates. He said Arndt knew a Frank Castro from med school.

In fact, authorities were able to track down Frank Castro, an orthopedic surgeon. Castro and his office manager explained that he had been in surgery in Tennessee for the entire time of the incident. Informed of the parcel containing narcotics that had been addressed to him, Castro told the inspector that of the few people he knew in Boston, "only one could be desperate enough to do something like that." David Arndt. He said he and Arndt had been friends since they were lab partners during their premed days in San Francisco but had not been in touch in some time.

David Procopio, spokesman for the Suffolk County district attorney's office, says that while the investigation is ongoing, Castro has been cooperative and "the only person against whom charges are warranted, according to the evidence now in our possession, is David Arndt."

Because of the new charges, Arndt was found to have violated his bail on the Cambridge case and it was revoked. (Earlier in the summer, Arndt had been found at Logan Airport carrying at least $12,000 in cash and his passport. The passport was revoked, but he was allowed to travel in the United States.) He would eventually be released, after posting $50,000 cash bail. But for two months, home for the surgeon and son of privilege was a cell in the Nashua Street Jail.

One weekend after the blizzard of headlines, Stephen and Jenifer Lipson went out to brunch and bumped into Ken and Anne Arndt. (Ken, by this time, had left his post at Beth Israel Hospital for a private practice in Chestnut Hill.) "We sat at our separate table, formally said hello to one another," Lipson recalls. "But clearly nobody wanted to talk about David. It was too sensitive."

What does Lipson think happened to his protege? "I think somehow he got involved in drugs and it ate him alive and he went over the edge," he says. "Beyond that I don't have an answer. And it's a shame."

If, as friends say, David Arndt has always viewed himself as the star of his own drama, what, in the end, drives the story line? Is his a story of downfall by drugs?

It should be noted that neither of Arndt's criminal cases has yet gone to trial, and he has pleaded not guilty to all charges. But if the allegations turn out to be true, he would hardly be the first hard-driving doctor to get wildly off track because of a substance-abuse problem. John Fromson is a Harvard psychiatrist and president of Physician Health Services, the Massachusetts Medical Society offshoot that provides support and monitoring services for doctors battling substance abuse and mental health difficulties. Confidentiality rules prevent him from discussing any one case, or even confirming a particular doctor's involvement with the program. But he has gained considerable insight from overseeing a program that has worked with about two thousand Massachusetts doctors over the last ten years.

This is not a great time to be a doctor. More than 40 percent of physicians surveyed in 2001 said they wouldn't go into medicine if they had to do it over again. With increased productivity demands and a tightening financial squeeze, doctors are under tremendous stress, and more of them are turning to drugs and alcohol for relief. An estimated 8 to 14 percent of physicians have a substance-abuse problem. In Massachusetts, surgeons are among the most affected.

Fromson ticks off the warning signs: verbally abusive behavior, tardiness, unexcused absences, inappropriate sexual behavior. The signs of strain tend to come first in a doctor's personal life. "When things happen at the workplace," he says, "usually they have been going on for a long time." Even then, he says, the problem may not be confronted, because most doctors are self-employed and only loosely supervised, and hospital management is often hesitant to call doctors on questionable behavior for fear that they will take their patient base to a hospital across town.

All of this means a doctor's substance-abuse problem can go unchecked and then trigger a downward spiral.

And if the drug of choice is crystal meth, or speed as it's also known, the narcotic at the center of Arndt's charges, the spiral can move at dizzying speeds. In his job with the San Francisco Department of Public Health, Grant Colfax has done some pioneering research documenting the prevalence of speed in the gay community. "For many gay men, crystal meth has just completely destroyed them," he says. "People bottom out. It's a question of how far down you've fallen, and if you can get back up."

"If you look at David's personality, speed is the dream drug," Colfax says. "It makes you feel invulnerable."

At some point in conversations about him, just about all of Arndt's friends and colleagues use that word or others like it to describe him and his self-image. Bulletproof. Subject to his own rules. Unbreakable.