The memoir “All at Sea” begins with a scene out of a parent’s nightmare: On a lazy late-spring morning, a little boy, still in his pajamas, is playing with his father on the beach. Minutes later, the child’s mother, looking out from their vacation house, sees a small head bobbing in the water. Her terrible realization is followed quickly by relief — the boy’s father is there to help, right? Then, suddenly father and son are pulled out by the current, and the mother dives in after them.

If you’ve seen a horror film — or a swim-safety video — you know where this is headed. Only two people return alive: mother and son.

“How could this placid little corner of the bay, no bigger than an average garden lawn, have stolen a man’s life?” asks that mother, Decca Aitkenhead. That it could — and did — is the sensational, devastating story that draws you into Aitkenhead’s book. What keeps you there is its author, a writer for the Guardian whose voice is like that of a wise and witty friend. Aitkenhead doesn’t play her story for tears or sentimentality. “The trouble with sadness is that it seldom produces anything new to say,” she comments. And yet despite herself, she has done just that.

It would be easy to dismiss Aitkenhead’s book as yet another volume on the weeping shelf of misery lit. But cast that cynicism aside. “All at Sea” is more than the recounting of a freak accident and its consequences. It is a thoughtful and provocative rumination on love, family and grief. Where “When Breath Becomes Air” offered a dying man’s perspective on mortality, “All at Sea” offers a widow’s perspective on survivor’s guilt.

All at Sea" by Decca Aitkenhead (Nan A. Talese )

The drama of Aitkenhead’s tale swells beyond the accident that upended her life. Her partner, Tony, was a neighbor who became a lover and broke up her marriage. He was also, when the pair met, a crack addict and a drug dealer. “Running off with the neighbour was the laziest marital plotline of every cheap sitcom,” she writes. Even more ridiculous, she confesses, was her hope that he would change his life for her. That Tony eventually does adds another layer of bittersweetness to an already sad storyline.

So too does Aitkenhead’s undiminished affection for the father of her two young sons. “Tony’s determination to enjoy himself was contagious,” she writes, “and made me a sunnier version of myself than I would have believed possible.”

By the time the couple and their children set off for Jamaica for their last vacation together, Tony had completed his university studies and had been working for a social service agency, helping neglected and abused children. Living in a charmingly dilapidated farmhouse in the British countryside, “I thought we were the luckiest family alive,” Aitkenhead writes. And yet, she adds, looking back, “every moment now seems so laced with menacing pathos.”

Alternating between past and present, Aitkenhead offers a rich accounting of her family and her interior life. She writes candidly of the difficulties of taking care of her children alone (“The urgency of the boys’ needs is inexhaustible, and the effort of will required to conjure a reassuring presence of maternal competence comes close to dismantling me”) and delves into her complicated relationship with her mother, who died just before Aitkenhead’s 10th birthday. “When someone dies young,” she observes, “the bereaved take comfort in a degree of posthumous deification.” In the case of her mother, that veneration became “rather like a video recorder, taped over my own memories until they were all gone.”

The author Decca Aitkenhead (Shakira Kleiner)

Aitkenhead hopes her children will not experience the same erasure through idolization. It is part of the reason she has written this book. Even as she acknowledges that “deification is inevitable” (as she notes, “Tony gave his life to save his son”), she wants them — and us — to also know his flaws, and her own. This honesty and flair for droll self-deprecation make Aitkenhead’s memoir accessible and inviting, never mind its dark subject. “I am shouty and inconsistent, joyless and volatile, and shaken by how quickly I have unravelled into the screechy stereotype of a single parent,” she admits.

Aitkenhead shuns pity — and this may be the greatest challenge to her readers, especially given a coda not included in the book: About a year after Tony’s death, Aitkenhead was diagnosed with breast cancer. It’s a twist that sets forth in her a new level of gallows humor and grace. “Until everything goes wrong, one cannot possibly know the astonishing kindness of the universe,” she wrote in the Guardian in March. “If my children have learned anything, it is that their world is full of people who love them, and perhaps this is a more precious lesson than any promise of good luck.” As for herself, she writes: “I’m not sure I would conjure my old assumption of good fortune back, even if I could, for it looks like hubris to me now.”

Aitkenhead’s book is a bracing and valuable reminder of the vagaries of fate that can leave you feeling unaccountably grateful — not only for your own relative serendipity but for the wisdom borne of Aitkenhead’s grit.

Nora Krug is an editor at Book World.

all at sea
A Memoir

By Decca Aitkenhead

Nan A. Talese/Doubleday. 225 pp. $25