The first victim the doctor approached was a slender young woman, her legs exposed and bloody where she fell after the explosions: at the edge of Boylston Street near a mangled stroller and toppled barricades.
Dr. Natalie Stavas performed CPR with the help of a stranger until paramedics arrived and loaded the woman, still unresponsive, onto a backboard and headed for the hospital.
Stavas, 32, had been near the finish of the Boston Marathon herself. She was covered in sweat and Gatorade, shivering, with numbness descending into her legs.
"I didn't feel anything," she later recalled.
She kept moving on to other victims. She plugged the gaping groin wound of a woman in her 30s with a borrowed T-shirt. She used other bits of clothing to stanch the bleeding from one man's mangled foot, and another's broken calf bone.
Then police, fearing another bomb, forced her to leave.
With no one to treat, Stavas was suddenly feeling things again: a rush of responsibility, guilt for not doing more.
"As a physician, I take an oath to do the best I can," Stavas said at her apartment in Boston's South End last week, stifling tears.
Before she left Boylston, Stavas snapped a photo with her cellphone of the spot where she treated the first woman.
A week later, more than 50 bombing victims were still recovering in Boston hospitals, and many more, like Stavas, are grappling with the emotional and psychological toll of the attack.
Stavas is not easily shaken. She is not normally a crier — she likes to tell people she didn't cry in "Titanic" or "The Lion King." The daughter of a doctor and nurse, the oldest of five raised in a Nebraska farm town, she knew what she was getting into when she embraced medicine. She was a trauma nurse in San Diego and Chapel Hill, N.C., and then became a pediatric resident treating some of Boston's neediest children through the joint program at Boston Medical Center and Boston Children's Hospital.
She is slender and petite, her hair a tumble of blond waves. She works 90-hour weeks. In her spare time this year she was teaching spin aerobics classes to fellow residents and training to run the Boston Marathon with her dad, her fourth time in the iconic race.
When she broke her left foot training weeks ago, she let her doctor know she still intended to complete the marathon. She was running for charity, and couldn't let her father down.
Despite her injury, she was on pace to finish that day in 4:09 (45 minutes slower than her personal best) when she approached the corner of Boylston and heard the blasts.
Her father was with her at first as she sprinted toward the wounded. A police officer stopped her.
"I'm a pediatric physician — I have to get to the scene!" she shouted. The officer let her through. Stavas hopped a 4-foot barricade and went to work.
"She was like an Olympic runner — I couldn't keep up with her," recalled her father, Joe Stavas, 58, a radiologist, who also helped treat fellow runners.
After being ordered away, she walked to the nearby Colonnade Hotel, where she found her mother in the lobby, sobbing. Unable to reach her daughter or her husband, she had assumed the worst. Soon after, Stavas' father arrived. Then the hotel was placed on lockdown as the area was searched for explosives. It was hours before Stavas finally returned home to her South End brownstone to rest.
Sleep brought nightmares. She relived her struggle to reach the wounded: An officer stopped her, she passed him but he trailed behind her, somehow slowing her down.
"It was just this recurring theme: that I had to get there," Stavas said.
She was supposed to work a 28-hour on-call shift Tuesday, but was allowed to postpone it. She called her parents at the gate at Logan International Airport and asked them to stay.
"She was shaken and kind of still in shock," her father recalled.
Stavas was by now known as a symbol of Boston's heroism and resilience. She spoke with reporters, some of whom tried to get her to describe the first woman she treated, believed to be one of the two women killed. She refused, for privacy reasons.
The pediatric resident returned to work Wednesday at Boston Medical Center, which treated a dozen of those wounded in the bombing. Although Stavas was not involved with their cases, she was reminded of them every time she entered the hospital and passed the slew of added police, huge men dressed all in black. She gave the hospital's pediatric emergency department the money she raised running the marathon, $6,000.
The next day, she attended the marathon memorial service at the Cathedral of the Holy Cross. As a first responder, she was ushered up front and seated amid a sea of firefighters, which she found comforting. The service became like a funeral for her, a time to mourn the victims."
It was very cathartic," she said. "I've been living with this sort of pit of grief inside me."