TONY Wilkinson was 49 when he drowned saving his son from the sea off a beach in Jamaica, a little after 8.30am on May 15, 2014. These are the facts of his death, reduced to a Tweet.

In its reporting of the accident, the Guardian newspaper carried the same information in a 10-word headline. In any paper on any day you'll find similar “stories”, accidental deaths condensed into a few sentences with perhaps a testimonial from a dazed friend or a matter-of-fact statement from a family member.

In this context, the name of the dead man's partner is just one more detail. But for The Guardian it was anything but because she was journalist Decca Aitkenhead, one of the paper's star writers. And so it found itself reporting dispassionately on something which affected it deeply, while Aitkenhead had the reality-melting experience of seeing the father of her children die in front of her, then reading about it in her own paper. Over the course of a few minutes, a dream family holiday had been turned into one of those it-only-happens-to-other-people nightmares.

For anyone living through one of these events, 10 words or a Tweet may be enough to capture the bare facts but they can never encompass the accompanying feeling of shock and emotional horror. Tens of thousands of words can't do it either, though in the months that followed Wilkinson's death, Aitkenhead gave it a go.

The result is All At Sea, a memoir of sorts about Wilkinson's life, his relationship with Aitkenhead, the emotional, practical and psychological effects his death had on her, and her experience of losing her own mother to cancer when she was nine. The dedication is simple but touching: "For Tony. You always said I should write a book about you. It wasn't meant to be this one”.

Aitkenhead wrote All At Sea, she tells me, because “every other aspect of my identity had just gone. I found myself a single mum and a widow and these weren't identities that I recognised had anything to do with me. So the impulse to write was also a way of hanging on to the one bit of me that I could still recognise and which hadn't been swept away.”

She started work on what would have been Wilkinson's 50th birthday, January 4, 2015, and quite coincidentally finished on the first anniversary of his death. The result is a book which is raw and immediate but also considered, analytical and, the hardest thing of all to pull off, devoid of self-pity.

“Obviously it's about Tony's death and my response to it, but I didn't have any particular need to pour out my heart and share chaotic feelings of grief. I was more interested in reporting or describing the psychological revelations that came from his death and the insights that followed from it. That felt easier.”

The forceful opening chapter, written in the present tense, deals with Wilkinson's death, starting with the moment he steps out of their holiday house in Jamaica's Calabash Bay to drink his coffee on the beach.

The couple's elder son, four-year-old Jake, goes with him. The normally glassy bay is choppy. Jake can't swim and isn't wearing his life vest. The next thing Aitkenhead knows, she's watching a head bobbing in the water and realises it's her son. She runs for the water but Wilkinson, not a strong swimmer, is already in. He reaches Jake and seems able to stand. Then he doesn't. Then he's struggling to stay afloat and waves are breaking in his face.

Now Aitkenhead is in the water too. She reaches Jake and takes him, struggling against the fierce undertow but eventually able to make it back to shore. But when she turns, Wilkinson is even further out. Now he isn't even trying to swim.

There is commotion on the beach. Rescuers do finally reach Wilkinson and, using a float, are able to bring him to shore. Aitkenhead expects him to sit up, but he doesn't. She expects his eyes to open but they don't. Then Jake asks his mother about the white stuff coming out of his father's nose, and a friend checks for a pulse. There's a shake of the head. “Has Tony died-ed?” asks three-year-old Joe, Aitkenhead's younger son. Yes he has, she tells him.

The reader Aitkenhead had in her mind as she wrote All At Sea was her friend Jenni Russell, also a journalist and one of the first people to fly out to Jamaica to be with her after Wilkinson's death. But of course the boys were in there too – or at least “hypothetical boys, not the boys I know now, who were three and five when I started the book. Obviously they'll be more than 10 years older than that when they read it, so you're writing for the boys you don't yet know, which is an odd thing”.

As it is, she says, “Joe can't remember the day Tony died, and if I ask Jake he says, 'I remember him just lying there'. And it's quite possible that Jake will remember that snapshot for the rest of his life. I don't think Jake can remember much else, but that will live with him.”

At home, Aitkenhead's job is to “keep the conversation going and open … keep Tony's name and references to Tony going so that he remains an everyday part of our lives.”

Within the family and among close family members it's easy enough. Outside the home, among friends and acquaintances, it's harder. “Jake can't stand it when people put on their special Tony voice, slightly hushed, slightly reverent, slightly tense. He wants him to be talked about in a very relaxed, easygoing way.”

Thinking back to her own experience of losing her mother, Aitkenhead can understand completely. “I think, 'God, I wish the grown-ups around me hadn't colluded in this collective fiction that children can lose a parent and they can never be mentioned again and we can carry on as if nothing has happened and this isn't going to be a life-long torment'.”

All At Sea was published in the spring and Aitkenhead has already appeared on several public platforms discussing it. Later this month she'll do it again at the Edinburgh International Book Festival. I ask her how she approaches what is essentially an act, a performance for people who may be recently bereaved themselves and who might expect a note of positivity.

“I'm not going to sit on the stage and cry or sob or behave in a way which is congruent with how I feel most days when I wake up,” she says. “I think that's not really on. If you've written a book and people are coming to hear you talk about it, it behoves you to meet them in a register which is suitable and not just be a sobbing mess.

"Simply being able to talk about the experience very openly and freely and being able to analyse all of this ... I guess that in itself is a hopeful message in that I certainly couldn't have been able to do that any time soon after Tony died. And it's a form of healing or survival to be able to talk about it all without feeling that you would go under. If I can offer positivity it's that."

And what kind of questions does she expect to get? Based on previous experience, “almost invariably someone asks me if I can feel Tony's presence as a ghostly spirit and whether I'm now a spiritual or religious person. The funny thing is, when I tell them that I wondered if that would happen but it hasn't they tend to insist that it has”. She cackles merrily at the thought, a rare moment of levity. “I don't know why. People don't take my word for it.”

So All At Sea is the book Decca Aitkenhead wasn't meant to write. But the one Wilkinson said she should write, the one she alludes to in that dedication to him, would have been equally gripping. His was an extraordinary life story.

The couple met when Aitkenhead and her then husband, a press photographer, moved to a new house in Hackney in London. Wilkinson, a tall, handsome, mixed race man with dreadlocks and an easy manner, was a neighbour.

He was also, as Aitkenhead discovered during their slow coming together, a drug dealer, crack user, sometime football hooligan, ex-prisoner and teenage runaway whose biological father was probably Jamaican but who had been given up for adoption by his 15-year-old white mother when he was just 18 months old.

Like Aitkenhead, he was married when they met. Unlike her, he had burgled his first house at the age of four (“It sounded impossible but he was adamant,” she writes), was working as a hustler in London by 15 and was still in his teens when he stood trial for shooting a Jamaican pimp. Sentenced to 14 years, he served five. By any yardstick, they made an unlikely couple.

After his death, it turned out that Wilkinson had turned an outhouse in their rural Kent home into an industrial-sized marijuana farm. Other than that, he was more or less on the straight and narrow. He had developed a taste for academia (he won a scholarship to study psychology and criminology at Westminster University) and found a calling of sorts working with Kids Company, the pioneering (but now defunct) organisation set up by Camila Batmanghelidjh to help deprived children in London.

And of course his last act was to save his son from drowning.

That odd duality – criminal and crack user versus doting father, reformed man and hero – is one Aitkenhead feels her sons might struggle with as they grow and try to accommodate their father's personality and life story into their own notions of who they are. Will they feel anger that he isn't there? Hopelessness at their situation? Pride at their father's achievements? Or will his troubled early years excuse any errant behaviour on their parts?

Aitkenhead hopes she can be there to guide them and help shape their memories, though that isn't a certainty: three weeks after she had handed her completed manuscript to her publisher she was told she had breast cancer. It hadn't spread to lymph nodes, brain, lungs or liver, but it was a type three tumour, the most malignant. With that diagnosis the chapter in the book that she says was the “second least hard to write”, the one dealing with her mother's death from lung cancer, suddenly acquired a terrible new significance.

Aitkenhead had already uncovered one family secret during the writing of All At Sea when she learned from her father that her terminally-ill mother had killed herself. Now she had a family curse to contend with too: an inherited genetic predisposition to breast cancer.

“It just felt like I was fighting a losing battle,” she tells me. “The odds felt so stacked against us that my impulse at that point was just to give up. I thought there's no point. This family is clearly just a busted flush and for reasons that I can't understand we're finished. I'm going to die of this, the boys' dad's dead, everything's over. Had Tony been alive I'm fairly confident that would not have been my initial reaction to the diagnosis. I would have seen it as something I had to get through. But to be honest it completely finished me off”.

And the thought that she might die of the same disease as her mother brought with it another realisation.

“I realised to my absolute dismay that I had begun to really emotionally distance myself from my children. There was no outward display of rejection, but inside I was withdrawing or protecting myself emotionally because the prospect of loving them as much as I did and saying goodbye to them was literally unbearable. And the only thing I had any influence over was how unbearable I found it.

“I am confident that that happened for my mum as it did for me and that explains some of my sense of detachment from her and why I withdrew in turn. I think I mirrored her emotional withdrawal, and that helped me not mind when she died.”

And so what should have been a second year of widowhood in which the pain of loss at least became more familiar became instead a year of chemotherapy and surgery. Aitkenhead had a double mastectomy, lost her hair, had someone else's glued to her head (it's called hair replacement therapy) and got her eyebrows tattooed. It would take many more words, 10s of thousands of them, to set out the many circles of hell the process took her through.

And the prognosis? “The likelihood of me still being alive in five years is really high, 95 per cent,” she says, almost breezily. “They say basically go away, take Tamoxifen for 10 years, live healthily and hope for the best.” And she's happy enough with that. “The point is none of us know if we're going to be alive next week far less in 10 years time so on one level how can I ask for more? And God, if Tony's death taught me anything it is that life is fragile and precarious and death comes quite randomly.”

For now, at least, there's solace in uncertainty.

Decca Aitkenhead is at the Edinburgh International Book Festival on August 22 (4pm); All At Sea is out now (4th Estate, £16.99)