She carries a knife in her backpack. She plans to plunge it into her heart. "And I could do it," she tells me quietly, with a confidence that makes me shift in my chair. She's in chronic pain, has been since the accident to her leg six months ago, but now, she says, it has broken through, so piercing she can't focus, can't think of anything but death. My job is to keep her alive while my colleague, a pain specialist and friend, works to find something effective. "There's too much left to try," he has told me.

She's 34. Before the accident she was a prominent attorney, fiercely bright, racing toward partnership with the single-mindedness of a Navy cutter. Meeting her today, you'd think she was a soccer mom, auburn hair framing high cheekbones, a golf shirt with a tiny jelly stain from one of her kids' sandwiches on her sleeve. She has that familiar, weary attractiveness, like so many of the women in my age group.

I want to hospitalize her. "Yes," she tells me, sounding like a lawyer, "you can make me do the 48 hours in-house, but as soon as it's up I'll tell them I feel better, the whole thing seems like a dream now. And once I'm out I'll do what I planned."

"And," she says softly, lowering her eyes, "if you hospitalize me against my will I won't work with you again."

This isn't one of those cries for help I've come across before: shallow cuts on the inside of an arm or taking a few too many pills. I know she's serious. She has been rehearsing -- driving to an isolated spot with the knife in her backpack, drinking heavily and holding the knife over her chest.

When I was finishing my training at McLean Hospital, a psychiatric hospital affiliated with Harvard, a girl on one of the open-door units hanged herself from a fire escape. She was in one of my groups. She'd gathered her bedsheets and quietly walked outside. They found her a few hours later. She was only 17. And now, sitting here in my office, I can see her face, her eyes and the gentle slope of her cheek, as if she'd just left.

"Could you page me if you're about to do it?" I ask.

She won't answer.

Our session did not start gently with talk about weather, parking or the slowness of the elevator. She followed me from the waiting room to my office, sat down, dropped her backpack and muttered, "What is there to say?" It has been like this lately. She starts with "Why am I here?" or "You can't really help me." And her hopelessness fills my office like a cloud of suffocating ink.

She knows my history. That my training as a psychologist was interrupted by cancer. That I've had a bone marrow transplant. That I'm familiar with pain and the hopelessness of a horrible prognosis. I've been writing a book that has gotten some publicity, and some of my patients have heard about it. One afternoon she came in and said, "So, you're a writer." I swallowed hard. Therapy, after all, is about the client. It's not supposed to be about me. She asked about the strange title, "Mom's Marijuana," and I explained as best I could about my illness and about my anti-drug mother growing marijuana in the backyard to help me. I tried to redirect her, but like a cross-examining attorney, she peppered me with questions. Eventually, she knew the skeleton of my story.

Initially, it helped. My history legitimized me. She listened when I told her she was more capable than she thought of tolerating the harsh side effects of her medications. But now she resents it. She has lamented, "I must seem terrible to you; you fought so hard to live, and here I fight to die." And she has been right.

I've struggled with how to help her find a hope that I never really lost. Even when I was certain that I was going to die, even when it was confirmed by physicians, at least an ember of hope burned. Until now, I've believed that, with grit and hope, we can endure most things. It has been true for my patients, though not for her. For the first time in my career, I can't understand a patient. And so I've withdrawn to the safety of psychological theory and science.

I've tried cognitive-behavioral and dynamic approaches. Existentialist. Humanist. Interpersonal. I've referred her to a psychiatrist, who has put her on antidepressant after antidepressant. I've consulted my old mentor. But her mood has continued to march downhill. And the bottom is coming up to greet us, fast and dark. I feel a frantic urgency rising in my chest.

Now she calls me judgmental because as I talk I wag a finger. I invoke her children: Have you taped photos of them to the knife? No. Could you assure versions of yourself 10 and 20 and 30 years older that you're doing the right thing? No. And then, in the quiet between us, I feel as if I'm trying to sell her a car she doesn't want.

She counters, "You've no right to judge. You can't feel my pain, my losses." She's right and her truth stings. "You're disgusted with me." No, I want to say, but I am disgusted, and tired. "You affect me," I tell her. "Powerfully. I'll be devastated if you kill yourself. So don't do it." And inside I'm trembling for her and those children. And maybe myself, too.

I know I'm not supposed to let her see my disgust, my frustration, my anger, but they have seeped out. I find that in this foxhole of intensive care psychiatry, I do things I don't do elsewhere. I share what I feel for her, even when I don't want to -- especially when I don't want to.

Before she leaves she gathers her backpack and sighs. She stands up, thanks me for not hospitalizing her and whispers a promise. She'll page me if she's about to kill herself. She opens my door, then turns back toward me, curiosity in her face. "What will you say if I do page you?"

"Don't worry about that now," I tell her. But as the door closes I wonder too.