It was the winter of 2001 and ten years since the woman had lost her daughter. The Twin Towers had recently come down. The panic group had grown in size, but its original members had become oddly more calm and helpful to each other, as if their free-floating anxiety had finally taken form, and the rest of the country had begun to feel the kind of terror they’d felt every day for years. For the first time Zee could remember, people in the group actually looked at each other. And when the woman talked about her daughter, as she had every week they’d been meeting, the group finally heard her.

The world can change, just like that! the woman said.

In the blink of an eye, someone answered.

Tissues were passed. And the group cried together for the first time, crying for the girl and for her inevitable loss of innocence and, of course, for their own.

BIPOLAR DISORDER HAD RECENTLY BECOME a catchall diagnosis. While it had once been believed that the condition occurred after the onset of puberty (as it had with this woman’s daughter), now children were being diagnosed as early as three years of age. Zee didn’t know what she thought about that. As with many things lately, she was of two minds about it. She hadn’t realized her joke until Mattei pointed it out, thinking it was intentional. No, Zee had told her. She was serious. Certainly it was a disease that needed treatment. Untreated bipolar disorder seldom led to anything but devastation. But medicating too early seemed wrong, something more in line with insurance and drug-company agendas than with the kind of help Zee had trained for years to provide.

The world-famous Dr. Mattei had long since abandoned her panic group, leaving them for Zee or one of the other psychologists to oversee. Mattei had moved on to her latest bestselling-book idea, which proposed the theory that the daughter will always live out the unfulfilled dreams of the mother. Even if she doesn’t know what those dreams are, even if those dreams have never been expressed, this will happen, according to Mattei, with alarming regularity. It wasn’t a new idea. But it was Mattei’s theory that this was more likely to happen if those dreams were never expressed, in much the same way that those who cannot remember the past are condemned to repeat it.

Zee had often wondered about the woman with the translucent eyes who came back to the panic group only once after that evening. She wondered about her unfulfilled dreams, expressed or unexpressed, and she wondered if there was something that the daughter was acting out for her mother as she herself had stood on Route 95 and accepted a ride from a stranger heading south.

Zee was glad that the woman had left the group before Mattei had brought up her latest theory. The mother blamed herself enough for her daughter’s disappearance, wondering every day if she might have changed the course of events if only she’d given her daughter that one elusive thing she’d failed to provide-something tangible and even ordinary, perhaps, like that red dress in Filene’s window. Or the week away at Girl Scout camp that her daughter had begged for years ago.

No one understood the concept of “if only” better than Zee. She lived it every day, though she didn’t have to search to find the elusive thing. She thought she knew what her mother had wanted that day so many years ago, what might have helped lift her out of her depression. It was a book of Yeats’s poetry given to Maureen by Finch on their wedding day, and it was one of her mother’s treasures. Zee’s “if only” had worked in reverse. If only she hadn’t gotten her mother what she wanted that day, if only she hadn’t left her alone, Zee might have been able to save her.

LILLY BRAEDON WAS LATE.

Mattei poked her head through Zee’s door. “It’s so damned hot out there,” she said. “Oh, God, you’re not in session, are you?”

“I’m supposed to be,” Zee said, looking at the clock. It was three-fifteen.

Mattei was re-dressing as she spoke, kicking off running shoes and pulling on her suit jacket. She walked five miles along the Charles River every afternoon, weather notwithstanding. When she was overbooked, which was a good deal of the time, she had been known to conduct her sessions while strolling along the river, calling it a walking meditation, telling patients it would be easier to open up if they didn’t feel her prying eyes on them. A week after she started conducting sessions that way, every shrink in Boston was out walking with patients.

“God, not that agoraphobic again.” It was another of Mattei’s jokes. Fifty percent of their patients had some degree of agoraphobia, a phenomenon that made attendance poor at best and had lately prompted Mattei to start charging time and a half for missed appointments, though Zee seldom required her patients to comply with this new rule.

Mattei was trying harder than usual to make her laugh today, meaning that Zee must be frowning again. Zee’s natural expression seemed to be the type of frown that inspired joke telling, often from total strangers, who always felt compelled to make her feel better somehow. Just this morning an older gentleman who had neglected to pick up his dog’s poop in Louisburg Square had walked over to her and ordered her to smile.

She stared at him.

“Things can’t be all that bad,” he said.

If he hadn’t been older than her father, Zee would have told him to get lost, that this was her natural expression, and that a man who didn’t pick up his dog’s excrement shouldn’t be allowed to roam free. But instead she managed a vague smirk.

“So seriously, which patient?” Mattei was waiting for an answer.

“Lilly Braedon.”

“Mrs. Perfect,” she said. “Oh, no, I forgot, that’s you.”

“Not yet,” Zee said a little too quickly.

“Aha!” Mattei said. “Simple, simple. Case closed. That will be three hundred and fifty dollars.”

“Funny,” Zee said as Mattei gathered up her running shoes and left the room.

IT WAS LILLY BRAEDON’S HUSBAND who had originally sought help at Dr. Mattei’s clinic. People came from all over the world to be treated by her. Harvard trained, with a stint at Johns Hopkins, Mattei was a psychiatrist who had great credentials. She’d written the definitive article on bipolar disorder with panic for the American Journal of Psychiatry. She had also worked closely with a team of genetic researchers who had uncovered a correlation between the disease and the eighteenth chromosome, a substantial and groundbreaking discovery.

But then Mattei’s career took a turn. She became fascinated by a more popular approach to psychiatry. The book she wrote during her tenth year in practice, a folksy self-help book entitled Safe at Home, lifted her to celebrity status. The book was inspired by a Red Sox second-stringer she had successfully treated for panic. Her practical solutions to his terror were based on biofeedback, desensitization, and sense memory.

“The world is a terrifying place,” Mattei explained first to a local newscaster and later to Oprah. “And here is what you can do to stop being afraid.” The book was filled with sensory tricks, tips almost too simple to inspire much credibility: carry a worry stone, smell lavender, breathe deeply. The companion CD featured guided meditations, some with music, some including nature sounds or poetry. It even quoted the old Irish prayer (the one that basically tells you not to worry about a damned thing because the worst thing that can happen is that you’ll go to hell, but that’s where all your friends will be anyway, so it’s pointless to fret). Though Mattei herself was a loose fusion of French, Italian, and Japanese ancestry, with not a bit of Irish blood, for some reason she loved everything about the Irish. It might have been a Boston thing. She loved James Joyce and even swore she had read and understood Finnegans Wake, which Zee seriously doubted. That Mattei loved Guinness and U2, Zee did not doubt. Zee and her fiancé, Michael, had spent last St. Paddy’s Day at a bar in Southie with Mattei and her partner, Rhonda, and Mattei had held her own, drinking with the best of Boston ’s Irish. And just a month ago, Mattei had come back from one of her therapy walks sporting a pair of pink Armani sunglasses that looked very similar to a pair Zee had once seen Bono wear.