Reflecting on his childhood in the autobiographical novel In the Castle of My Skin, George Lamming wrote that it was “my mother who really fathered me”. Damningly, the Barbadian novelist asserted that his father “had only fathered the idea of me”. That notion of children being left mainly, if not solely, the liability of mothers still widely resonates in Caribbean households. In Kit de Waal’s tender novel, The Best of Everything, the protagonist Paulette, a single mother, embraces the role not just of mothering and largely fathering her son, but also selflessly acting as a proxy mother to a child who risks being abandoned.

De Waal, who edited the 2019 anthology Common People, has long championed working-class lives, “written in celebration and not apology”. In The Best of Everything Paulette is a migrant to Britain from St Kitts, an auxiliary nurse whose disdain for bedpans does not dampen the pleasure she takes from the thought that “it’s nice going home at night knowing you’ve helped people”.

At the start of the novel in 1972, Paulette, aged 29, is fervently in love with Denton, a Jamaican building contractor whose ambition is evident in his leather-seated, cherry-red Toyota. Busy, allegedly, with work abroad, his irregular visits heighten his appeal. Denton sleeps with an arm wrapped around her shoulders “like a fur stole”. Paulette scrutinises him, looking for possible faults, but all she finds are “things that make her love him more”.

Early on, though, Paulette’s excited plans for their future are shattered when Denton is killed in a car crash. De Waal uses spare, unfussy prose to capture Paulette’s grief, which receives scant recognition even from her friends. “Them with their side-eye … The rough questions with the smooth sympathy … lacing their interrogation with wine.”

The Best of Everything is a quiet, mournful book whose title speaks to everything that Paulette has lost: the chance to own a home, to start a family and give her child every scrap of love, to surrender to the man who was forever in her heart, to be “coaxed, kissed and caught”. Fate mocks her and the miniature bottles of Appleton rum that she begins to secretly knock back only partially anaesthetise her pain.

The fatal car crash is the animating incident powering the novel with a series of unexpected consequences. In the first instance, Paulette takes comfort from Denton’s best friend, Garfield. Pretty soon Garfield upgrades from sympathetic companion to lover, one who gives Paulette what she has yearned for: a baby.

The understated tone of the novel, perfectly judged through the elegant modesty of the writing, reflects the emotional veil that Paulette especially wears in public, with one notable exception. Walking through a park, with Garfield pushing their baby, Bird, in his pram, Paulette sees the elderly man whose dangerous driving led to Denton’s death. To the horror of Garfield and passersby, she leaps on the man and wrestles him to the ground.

The assault unsettles Paulette more than the target of her wrath; it’s contrary to her sense of decorum and of self. In demonstrating Paulette’s complexity, De Waal meets the difficult challenge of creating a kind-hearted protagonist who is caught in a conundrum of withholding emotion and surrendering to an internal migration while still being keenly attentive to others.

Paulette’s capacity for generosity is further tested later by another extraordinary encounter with the same old man from the park. Frank Bowen is a lost soul who “poured more disappointment into one look than Paulette thought was possible”. Frank mourns his daughter, a passenger in his car during the crash, who suffered a brain injury and died three years later.

In a theatrical plot twist, handled adeptly by the author, Frank corners Paulette and pleads with her to adopt his orphaned grandson Nellie. A disheveled Frank seems barely able to take care of himself, never mind a young boy. Nellie’s pitiful look “nearly splits her in two”, and within a short time she’s regularly inviting the boy into her home.

Till this moment, Paulette’s focus had been exclusively on Bird, but by the end of this beautifully rendered tale extolling unfashionably the virtues of kindness, Paulette acknowledges “an extra chamber in [her] heart” where Nellie resides. The admission is emblematic of a quietly unforgettable character, a compassionate, nurturing mother who also fathers the two boys. It’s her maternal Caribbean nature, “and there’s nothing she can do about it”.

• The Best of Everything by Kit de Waal is published by Tinder (£20). To support the Guardian and the Observer buy a copy at guardianbookshop.com. Delivery charges may apply.