When I heard a year ago that a man had been shot dead on the tarmac at Miami International Airport, I jumped to the conclusion—even in this era of terror alerts—that he was mentally ill, not a terrorist. It turns out I was right.

I'm a pediatric oncologist. My enemy is cancer cells—a white blur on a CT scan, a blue blob under a microscope. But that hasn't kept me from being drawn to psychiatry. How could I not be fascinated by patients whose enemy is their own minds?

When I was a second-year medical student, we met every Friday to practice our psychiatry interviewing skills. Patients volunteered to be our subjects. Most of them had clinical depression. They spoke in flat voices. Their faces showed no emotion. They took no pleasure in family, food, or sex. It pained us to hear their tales on those Fridays, as we anticipated weekends filled with parties and dates.

One Friday, 20-year-old Simon broke our streak of depressed patients. He had wavy hair and piercing eyes. The student interviewer—Mary, an earnest, religious girl—sat face to face with Simon.

"Why are you here?" she asked him.

"Early one morning I saw this amazing sky—red, pink, purple—and I thought, 'This must be a sign.' And then I heard God's voice."

Mary's eyes grew wide. "You did? What did he say?"

"He told me to follow him. He said that school and work were false paths and that my true calling was to follow him."

Screening: Mary went on to ask the usual psychiatric screening questions about appetite, sleep, mood. Simon's answers were unremarkable. Finally our professor ushered Simon out and returned to ask, "Mary, what did you think of Simon?"

"That was an amazing story . . ." Her voice trailed off.

"Yes, but what's wrong with him? What's his diagnosis?"

Mary hesitated. Simon wasn't a "diagnosis" to her. He was a young man, traveling alone, given a message from God. Finally she gave an answer in the

Illustration by Suzanne Dejohn

I concluded—even in this era of terror alerts—that the dead man was mentally ill, not a terrorist. It turns out I was right.

form of a question: "Is he psychotic?"

"Yes, very good. Simon is a schizophrenic. What he described was his first 'psychotic break.' The police found Simon at the bus station, dirty and disoriented, wearing nothing but a bathrobe."

Mary looked dejected as our teacher explained "downward drift"—that schizophrenics tend toward unemployment and poverty as a consequence of their disorder. I'm ashamed that I felt a perverse thrill knowing Simon had pulled gullible Mary into his delusion.

In 2001, John Walker Lindh, an American member of the Taliban, was taken prisoner in Afghanistan. I hastened to fill in his psychiatric history when I read that his parents were divorced and he came from tolerant Marin County, Calif. I figured that Lindh was schizophrenic and had found Islam after a psychotic break, that the Taliban offered structure missing from his life. Photos of Lindh did nothing to disprove my theory: emaciated, with a blackened face and straggly beard, he looked like a homeless schizophrenic.

But later reports described Lindh as a gentle soul who had found Islam as a teenager and whose parents loved and supported him. The press uncovered no evidence of mental illness. I wondered if sweet Mary had remembered Simon and assumed mental illness when she heard about Lindh; I felt cynical because I had.

Protect: As a third-year medical student, I did my psychiatry clerkship at an

inpatient facility. Sarah—a young woman in her early thirties, married with children—arrived there after an intentional overdose of alcohol and sleeping pills. She thought she was a Mafia target and that only when she was dead would her children be safe from the wrath of organized crime. I thought of her years later when I heard about Andrea Yates, who stopped taking her anti-psychotic medications and drowned her five children to protect them from Satan.

Then there was Josh, a muscular young man in his early twenties.

"Why are you here?" I asked Josh.

"I went to New York for the weekend and when I got back, I called my buddy from the airport to come get me, but he said he couldn't. I told him, 'That's bullshit. Get off your ass and come get me.' While I'm talking to him, some lady tells me to get off the phone because she needs to use it. I tell her, 'Shut up, bitch. Can't you see I'm talking to my friend.' She gets mad and goes to security. The guard comes and tells me to get off the phone. So I show them my duffel bag and say, 'Back off. I have a bomb in here and I'll use it if you don't go away.'"

"Did you have a bomb in your bag?" I dutifully asked him.

"No, I didn't."

I rephrased the question: "Did you believe you had a bomb?" "I knew my bag was filled with dirty laundry," he said. It turns out Josh had borderline personality disorder. "People like Josh have problems with behavior and interpersonal relationships," my professor explained. "They can be tricky to diagnose," he added.

Bomb: Which brings me back to Miami International Airport. Rigoberto Alpizar, a 44-year-old passenger, said there was a bomb in his carry-on. Federal marshals ordered him to the ground. When he appeared to reach into his bag, he was shot. Investigators found no evidence of a bomb. His wife later said her husband was bipolar and had not taken his medicine that day. I remembered Josh, knowing he could have ended up like Alpizar, whose death marked the first time a federal air marshal fired a weapon at an individual since 9/11. I hope marshals now receive training in how to recognize psychiatric illnesses. And I hope patients with mental illness take their medicine.