Valentine's day, 2006. Nelson hopes for a slow shift. But somewhere in Iraq, an Army convoy hits a roadside bomb and a medevac helicopter rushes in a seriously wounded soldier. The situation is going badly.

The soldier arrives medically dead. A tourniquet encircles the right leg. Below the tourniquet, the limb hangs by threads of flesh. The femoral artery is like a severed hose. There is the coppery smell of blood.

Nelson stands at the head of the bed, feeling for a pulse, giving directions. Medics slice away the remains of a uniform. Nelson realizes her patient is a woman. She has no pulse, she is drained of blood. Nelson orders someone to begin CPR, even though in her experience it has never saved anyone. A doctor calls for drugs: atropine, epinephrine. Nelson injects them into the woman's body. Finally, she feels the weak flutter of life. "After about five minutes of CPR, I felt a carotid pulse," Nelson later wrote in her journal. "We double- and triple-checked to make sure we weren't just so hyped up that we were feeling our own pulse in our fingers."

Nelson's team pumps blood into the woman; it runs out her shattered leg. To save the life, the limb must go. A surgeon slices. Someone loops another tourniquet around the stump. The team bandages the wound and preps the woman for the operating room, where surgeons will clamp off her artery, insert a chest tube, and clean shrapnel from her body.

After surgeons saved the woman's life, Nelson visits her upstairs in the intensive care ward. She finds the woman's husband at her bedside; the couple serve in the same unit.

"That was one of the more emotional cases I've had," Nelson says. "I think that's where I gained my confidence. With her, I felt I took charge. I felt I had peace of mind, I wasn't freaking out. And, on Valentine's Day, I didn't have to say, 'Your wife didn't make it.'"

Groves, her boss, noticed the change and kept her on. "Now she can do anything," he says, smiling. "She's brought people back from the dead. Our joke is if you come in dead, you want Nelson at the table."

After months in Iraq, Nelson and her colleagues have helped save hundreds of lives. They have seen more human wreckage than most of their stateside peers ever will. Their stained boots are badges of honor. In the late winter, it was common to hear young nurses and medics say, "I never want to leave." Older staffers shared the sense of purpose. Many said, "If it was a little safer and I could bring my family here, I'd stay." The work, the importance of it, was exhilarating.

By summer, past the halfway point in the 10th CSH's tour, those feelings have faded. A makeshift calendar hangs on the wall beside the nurses' station, each remaining day in Iraq marked on a slip of white paper. Home is not simply a place, it is a goal. Everyone yearns for a life less cloistered, closer to family and old routines, away from war.

Many have taken mid-tour leave. The two weeks' vacation either recharged them or intensified the desire to leave. "Before I went, I was not doing well," Nelson says. "I was starting to have dreams about patients, like, what could I have done differently." The break refreshed her, gave a boost she hopes will last till the tour is up. When I see John Groves again, after his leave, there is a new weariness, a heaviness in his face. "I'm ready," he says. "I think we all are."

The end will come soon enough, but heading home won't be simple. The memories will follow, and more. Groves worries that many of the young staff will be bored when they return to stateside jobs at base hospitals or troop clinics. "The medics and nurses here are doing things that only doctors do back in the States," he says. "I'm teaching 20-year-olds how to put in chest tubes. When they go back, they won't be able to do that stuff."

No one at Ibn Sina may ever feel as useful or needed as they do saving lives in Baghdad. It is not that the trauma crews hope for more wounded. It is not that they want the war to limp on forever. But they have an overwhelming desire to put their training into practice. The same can be said about medics like David Mitchell -- about almost any soldier doing medicine here.

"We're like vultures, kinda," a nurse explains late one night as we sit waiting for the thump of incoming helicopters. "This is what we do. We're not out there stopping the fighting, so we're waiting to go to work."

For them trauma is exciting. A cloud descends, blocking out the rest of the world. There is only the work, the bright red immediacy of blood. In the trauma room, a simple truth rises above the gasp of breathing machines and the high, frantic voices: Life is everything; it is all that matters. The details come later.

Part Two: Home Front

Jason Welsh held the phone close and lied to his mother. He told her he'd been in a car wreck in Iraq, but he was fine. "I think I broke my jaw pretty good," he said, "but that's all." The lie made sense. Telling the truth, that he'd been blown up by a roadside bomb, his neck was broken, his face smashed, that three men died beside him, somehow didn't seem right. Welsh, 25, remembers thinking, If I don't tell her, it'll be OK. It'll be like it didn't happen.

Lynne Welsh, listening in Oklahoma, didn't believe him. Her mind spun. Fear flooded in. "I was so scared my voice got weak," she says. "I finally asked him, 'How are your arms and legs?'"

The question reveals the dread of every military parent, spouse, girlfriend, or boyfriend. The answer would shape the Welshes' future. Dreams would survive, or shatter. "My arms and legs are fine, Momma," Welsh said, and that, as far as it went, was the truth. Some 20,000 American service members have been injured since the war in Iraq began in 2003. Medical technology and the sheer speed of rescue and treatment have increased soldiers' chances of surviving wounds that would have killed them in previous wars. But any notion that body armor and medicine have somehow made this war safe is unfounded. Stacking armor on troops and vehicles has only bred more accurate snipers, more devastating bombs. Medicine, while more advanced than in previous wars, cannot wipe out the brutality of the battlefield.