It's 5am and Roderick Holohan has been prowling around the streets of Kings Cross for most of the night, looking for a suitable target. He's desperate, and now he's dangerous. As well as being a hopeless junkie out for a fix, he's also a diagnosed schizophrenic who has stopped taking his medication. He needs cold cash for drugs and he knows he's got it in him to do whatever it takes, to whomever crosses his path, to get it.

Young mum Samantha Barlow doesn't stand a chance. As she walks briskly past the start of Arthur Park, she can't see the dark figure slinking out of the shadows towards her. The first she knows of his presence is when she feels a blow, hard, to the back of her head, delivered with such force it actually dents her skull.

She crumples to her knees but the blows from the sharp edge of a rock keep coming. Her hands go instinctively to her head to try to protect it and her right hand is instantly smashed and mangled. There's blood pouring from the back of her head, her forehead and her face, matting her hair, a dark stain seeping downwards through her clothes. She keeps fighting back, still gamely hanging on to her bags. Finally she falls forward, face first, onto the ground.

The man tries to wrench the bags from her grasp and then, infuriated, smashes her face into the stone wall. At last, she goes limp and sinks into unconsciousness. At that, Holohan looks furtively around then, like a wild animal, grabs her and drags her into the back of the park to his lair, where they can both be hidden in the shadows, leaving an eight-metre trail of blood in their wake. He then rips open Samantha's leather bag and darts back to where items from another bag lie scattered on the ground. As he gathers them, he suddenly stops dead. One is a blue shirt, with the unmistakable epaulettes and crest of the NSW Police Force. Shit. This woman is police.

The surgery on 34-year-old Samantha took longer than anticipated because of the extensive damage to her scalp, the expectation that her skin might not survive and need grafts, and the risk of infection from the dirt, blood, pieces of brick and other debris that had penetrated her wounds during the attack. No one could say with any confidence that she would live and, even if she did, if she'd ever fully recover from her injuries.

"We were being told to prepare ourselves for the real chance that Sam would suffer some form of physical or mental disability for the rest of her life," recalls her husband, fellow police officer Laurence Barlow, then 45. "And there was still that distinct possibility that I'd soon be making funeral arrangements for my wife."

Even people who might, under normal circumstances, not be fans of the police were appalled. At Kings Cross police station, a steady flow of locals, including street workers, criminals, drug dealers, gang members and other "colourful" identities, dropped by to express their sympathy.

The then head of Kings Cross police, Superintendent Tony Crandell, was stunned by the reaction of the local community. "What I saw now was the poorest of the poor, the street prostitutes, the drug-addicted, the alcoholics, those people coming together to say to me, 'We want you to know this was not one of our community that did this, you must understand that we would not do this to our police.' "

At 9.15pm the night following the attack, a posse of police pounce on Roderick Holohan as he's sitting on a bench at a Wollongong railway station, south of Sydney. He's startled but doesn't seem surprised. The police have tracked him down to the nearby park where he'd slept, and then followed him. As he's arrested, he immediately admits to the attack on Samantha. "I thought I'd killed her," he says.

"Not yet," is the tight reply.

Laurence Barlow regarded the St Vincent's Hospital neurosurgeon Dr Malcolm Pell nervously as he approached, but he smiled and stretched out his hand. "He came in, shook my hand and, before letting go, told me his prognosis, that Sam was recovering well and he thought she was going to be okay," says Laurence. "I heard the words but couldn't accept them. I weakened my grip, teared up and looked at the floor. He responded by grasping my hand more firmly and repeating himself, staring at me eyeball-to-eyeball. He refused to let go of my hand until I acknowledged what he was telling me."

Yet Laurence still had trouble digesting his words. "I felt numb and in shock again, disbelieving Sam's recovery in such a short period of time," he says. "Three days before, she was on the verge of death. Now I was being told that she would probably live. It's all we ever wished for, but now I was too scared to embrace it."

The doctors had been gradually reducing the amount of medication Samantha was on and decided the time was right to finally attempt to bring her out of her coma. Originally, they'd predicted she'd be sleeping for 10 to 14 days, but the speed of her recovery had surprised everyone, and they saw no reason to prolong the process.

Laurence felt the hairs on the back of his neck stand up. This was the moment he'd been waiting for, hoping for, dreaming of, for the past four-and-a-half days, but suddenly he felt gripped with nerves. What if Samantha woke up and didn't know him, didn't know anyone? Would she still be the same woman he'd fallen in love with?

Suddenly, the curtains around Samantha's bed were ripped back. Laurence raced over. She was struggling to open her still badly swollen eyes but as she finally managed to open them, he could see her looking around. As her eyes finally settled on him, he saw the flicker of recognition, and realised she was trying to move her body and her arms towards him. Laurence's vision blurred and he felt a heady sense of euphoria completely engulf him.

He kissed Samantha and held her hand, then hugged everyone within arm's reach, over and over again. Samantha was back again; they were being given a second chance at life.

"Words couldn't describe my sense of elation and relief. It was as if Sam had been reborn. She had the worst black eyes in the world, her nose was still broken and her head was still in such a huge bandage you could only see the smallest amount of skin, but she knew me! She was back!"

But Samantha still had a long way to go before she was completely out of danger.

"It was a scary time," says Laurence. "The doctors explained to me that it was like a computer being rebooted, and her cognitive recovery would be uneven as everything came back into line. It was hard seeing how bewildered she could be, and then stressed because she couldn't remember stuff. We were all delighted she was alive, but the next phase of her assessment and recovery was not whether she would suffer significant mental and physical disability; it was how severe it would be."

In fact, it quickly became apparent that Samantha knew absolutely nothing of the attack. "I can remember setting out for work that morning, parking the car and walking up the hill, then ... nothing," says Samantha now. "A big blank."

The day after she woke from the coma, Samantha was shown photographs of her children Lily, then two, and seven-month-old Ben. She asked who they were. She'd even forgotten she had children. Gradually, she came to recognise Lily, but Ben was still a mystery to her, and stayed that way for a good week after the coma.

Samantha was given a battery of tasks to complete to try to push the slower parts of her brain into action, or to test whether other areas were firing normally. They required enormous levels of effort and concentration and she tired easily. Yet she was always determined to do more, to try harder, to see if she could succeed in clearing away more of the fog clouding her brain. She requested additional memory tests and pressed Laurence to ask her questions, and she seemed to be constantly processing the information she was being given.

But too often, and without warning, the "real" Samantha would slip away and a stranger would appear in her place.

"Sometimes, it was as though an alien had possessed my wife's body, like Linda Blair's in The Exorcist," says Laurence. "One minute, Sam would be capable of superhuman things, then, in a split second, her personality could change to a completely different character. I'd be talking to her, then Sam would go off on odd tangents, as if she had multiple personalities. I'd tell her what had happened to her, then she'd accuse me of lying to her and interrogate me relentlessly in a character I came to think of as 'Sergeant Sam'. Then she'd switch to worrying where her belongings were, like jewellery, her phone and the bag she'd had taken.

"There were moments, too, when she'd get angry and fire up, trying to get out of bed, and start trying to swing her arms, saying again that she wanted to 'get the bastard' who did this to her. Then she would act and talk like a police sergeant asking questions about the investigation. The final emotion each time would be tears and a sense of uselessness, blaming herself regardless of anything I would say.

"I found myself lying awake at nights wondering what the hell our future looked like," says Laurence. "I was trying to hold everything together but at the same time, I was dying from the inside out. The anxiety became all-consuming, preventing me from sleeping. My self-esteem and confidence were shot to pieces and I was scared of myself ... I was scared that the rage I was continuing to suppress about the man who'd put us in this position was going to bubble to the surface and I was going to do physical harm to someone. I was losing it."

It was so difficult to behave normally in front of the children, too. Lily, in particular, was suffering extreme separation anxiety. If Laurence told her that he was off to work, she was clingy, but okay. If he said that he was going to the hospital, she'd scream, cry or withdraw completely. In her world, the place she called "hobsital" was where mummies went - and didn't come back.

Roderick Holohan, 39, Samantha's attacker, was sentenced to a total of 21 years for the assault on her and other offences. Three months later - 22 months after the bashing and following extensive rehabilitation - Samantha was finally allowed to return to work.

While she loved being back, she also had to admit that things were different from what she had so fondly remembered. She had been to hell and back and was still struggling physically and psychologically, living on a maximum of three hours' sleep a night, trying to cope with post-traumatic stress disorder, brain injury and clinical depression, and still having to undergo rehabilitation sessions.

As much as Samantha avoided admitting it, she knew she was having problems with the job itself, too. Although she'd been working with a psychiatrist to overcome them, she was still haunted by ghosts from her attack. She no longer enjoyed working alone in a car on highway patrol. Her loss of her senses of taste and smell, from her brain injury, also became an issue almost straight away. One busy morning there was a gas leak in Darlinghurst and the call came for a highway patrol supervisor to take charge of traffic management. Samantha accepted the job but, as she drove there, she realised she'd have no idea if the gas smell grew stronger, and handed it to someone else instead. She knew she'd be similarly in trouble managing traffic if ever there was a petrol leak.

Her boss, Tony Crandell, felt that this was a huge limitation on her abilities as an operational police officer. "That really hit home to me that she had some serious issues," he says. "She would have had a limited time on the street, and that would have hurt her no end. She's not a desk-bound cop like me; she always wanted to be, and always would be, an operational cop."

Then there was the issue of alcohol- or drug-affected drivers. Often, in court, the police officer who stopped a driver would be asked if the defendant had smelled of liquor or cannabis; she wouldn't have a clue.

The other thing Samantha was struggling to hide from her colleagues was that her body was not coping well with some of the challenges: "Despite all the hard physical training I'd been doing, there still seemed to be a difference between being fit and being 'match fit', " she says. "It was hard to admit to myself, but my body simply couldn't do it any more."

Samantha reluctantly applied for a medical discharge and took some time out. Even though she hated the thought of being forced out of a job she loved, she'd fallen pregnant with a much-longed-for third child, and relished the chance to rest and spend more time with Lily, now 5, and Ben, 3.

She'd had a near-perfect pregnancy, with little morning sickness and no complications. The children were thrilled about the prospect of a new baby girl about to join them, and came along to a routine scan at St George Private Hospital, six weeks before her due date. They duly turned up in January last year ready for a quick scan, then lunch and a visit to the cinema. It was never to be. The nurse examining Samantha announced she could find no heartbeat from the baby. They all stared at the monitor. Their precious daughter had died overnight, at 34 weeks.

Harper Elizabeth Barlow was stillborn at 6.30pm that evening by emergency caesarean. She looked perfect, with a full head of brown hair and a rosebud mouth. An incredibly active foetus, her umbilical cord had apparently become so tightly twisted, it had cut off the flow of blood and oxygen from mother to daughter.

Looking back, Samantha feels she took Harper's death much harder than her own near-death.

"It was just so sudden," she says. "If we'd had any indication that something wasn't right, we would have been prepared, but we didn't. It was really mean in the sense that one day everything was fine, and the next, she was gone. To have gone so long and been so close ... that's just wrong. Harper was so perfect and she was supposed to be the last part of our family to make it complete.

"For a while, I thought I'd done something wrong. Maybe there'd been something in my food or fish, or I'd taken too much magnesium. I probably had two sips of wine throughout the whole time, and I thought it might be that. Or maybe I was too active. But I'd worn a heart-rate monitor all the time I was pregnant to make sure I wasn't stressing my body. And my body had been through so much, who's to say that my injuries didn't play a role? In the end, I had to finally accept it was just one of those things you don't have any control over. It's just pretty unfair that we got smashed again."

Samantha's farewell from the police force in August last year turned into a major event. More than 100 people attended the mid-morning ceremony at the Sydney Police Centre in Surry Hills. Samantha had served 18 years as a police officer, but was still desperately sad to be leaving.

"I worked very, very hard to get as much of my body back as I could, and I did do a good job," she told the assembled crowd. "But if you can't do 100 per cent, then you shouldn't be there. It's a very sad day. I hoped to retire from the police when I was 60, not to retire at 37. It's the best job in the world, and I'm very sad I'm not in it now."

NSW Police Commissioner Andrew Scipione responded by saying the vicious attack had robbed Sam of her destiny, and the police force of a potential leader. "She had a brilliant career and was, potentially, a police commissioner of the future," he said. Samantha's friends and family smiled at the thought of her one day possibly being a contender for the title of NSW's first female police commissioner. But now, no one would ever know.

Samantha still suffers from dizziness and has balance issues, particularly when she stands up too fast, bends down or is somewhere high up, and it might take 30 seconds or so before the feeling subsides. Sometimes her sight is blurred and her eyes take time to focus on what she's looking at.

"Whereas Sam once had no fear of anything and enjoyed pushing the boundaries, she is now far more cautious and says that things can hurt," says Laurence. "But the impact of her injuries on her daily physical life is minimal compared to what she did go through. People might complain about not getting a good night's sleep, but try to imagine what it's like not to be able to lie flat for 18 months and then not being able to sleep even three hours a night - sleep that's still regularly disrupted with violent dreams."

For it's not just the physical scars; the mental ones run even deeper. Samantha's close friend, Senior Sergeant Belinda Crowe, says she, like many of her friends, can see the evidence of them all the time. "Sam has changed," she says. "She doesn't share as much any more; you have to prise information out of her. She's a bit mistrustful of people and less tolerant."

Similarly, Laurence's friends see the changes in him, too. "When I first met Laurence, he was outgoing, friendly, very knowledgeable and a social type of person," says his good mate, Inspector Paul Condon. "But now he is different. We're not so close any more, not like we used to be."

Detective Sergeant Matt Moss, who headed the investigation into the attack on Samantha, shares this view: "He's very angry and he has every right to be. Everyone deals with their grief in a different way. That he's come out the other side is testament to his strength, and their strength together. They needed each other to get through this drama, but they laugh together and are very much in love."

Both Samantha and Laurence have been diagnosed with post-traumatic stress disorder (PTSD) and clinical depression, with Samantha also having to deal with the effects of traumatic brain injury. Laurence sustained PTSD from the years he'd spent on the police frontlines, including in the riot squad, but it's known that such a disorder often only comes to the fore when something happens to bring the individual to a complete standstill, as with the attack on his wife. And just as Samantha's deep maternal instinct drove her will to survive and then her miraculous recovery, it's also helping her overcome her problems now. Exercise has provided a powerful antidepressant, although there's no way of predicting what the long-term effects of the brain injury could be.

"That's the big black cloud that hovers over both of us," says Laurence. "We know only too well now that life can change completely in an instant, so living a long, healthy and happy life is now our biggest challenge."

Of course, there's still residual anger about the attack that cost them so dearly. On any street corner, when Laurence spies a group of drug users, he feels fury rise. "Sam was always more tolerant than I was," he says. "In my 30 years as a cop, I've seen a lot of drugs and the misery they caused. They'd steal the eyes out of the back of your head if they could buy drugs. I've always been in favour of zero tolerance. I think all drug users should be eliminated. You look into their eyes, and there's nothing there. I don't see them as victims. Everyone has a choice, they're chosen to go that way."

Yet now it feels like the couple have the chance of a new beginning, particularly with new baby Zac, born in February this year, to focus on. While the pregnancy was tinged with anxiety after Harper, and Samantha was on tenterhooks in the weeks before his birth, in the end everything went perfectly smoothly.

The couple are now happy to have more time to dedicate to Zac, Ben and Lily, although nobody knows what effect, if any, this has had on the two eldest. Recently while staying with her grandparents, Lily woke up in the middle of the night and asked, "Where's Mummy?" - something she'd never done before.

Yet youngsters often possess a great ability to accept things and move on. "We probably won't know until much later in life," says Samantha. "But hopefully they were too young to know what was really going on at that time. I think I'll wait a long time before I discuss what happened with them."

Edited extract from Left For Dead: A True Story of Resilience and Courage by Samantha and Laurence Barlow with Sue Williams, published by Penguin this week.

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