WHILE The Sorrows of an American was in gestation, Siri Hustvedt publicly confessed that she was writing it as her imaginary brother. Fully fledged, and however imaginary, this brother has much in common with the author: Norwegian immigrant ancestors; a father recently deceased, who fought in the Pacific during the Second World War (and recorded his experiences in a memoir); a rural Minnesota upbringing that led to an urbane adulthood in Brooklyn.

There are further parallels to be drawn within this illusory cat's cradle of fiction, memoir and biography. Yet any attempt to unravel the strands would be superfluous - and missing the point. As Hustvedt, via her counterpart, repeatedly reminds us, writing and remembering are dubious exercises. There is a fuzzy line between memories and imaginings, dreams and realities, feelings and ideas, objects and symbols, characters and relations.

The introspective, meditative and, at times, vertiginous narration seems necessary for Erik Davidsen: effete psychiatrist, middle-aged, newly divorced, in mourning and utterly joyless. His refrain “I'm so lonely” pauses only for doorstep encounters with his new lodger, a Jamaican artist called Miranda, and her wise pipsqueak Eglantine. Erik's altruistic attempts to win Miranda's heart are thwarted by her ex, a stalking photographer, not to mention her ambivalence.

The poignant What I Loved began with the found letters of a model-muse to her painter-lover. The spark here is Erik's discovery of a 1938 letter to his father Lars from an unknown Lucy, and the memoir - dropped into the modern-day story frugally but as forcibly as grenades. The most moving of these extracts are not the soldier's tales (though there are arresting moments; for instance an ambush on a Japanese soldier crouching, praying perhaps, in the grass) but those of the farm lad, who witnessed his parents' struggle and defeat during the Depression.

A Novel of Secrets, says the subtitle; inside, that tiny preposition becomes key. Though the actual secrets are no great shakes (particularly the Lucy one), no matter: this story is about their existence, their recovery and their traumatic effect upon families, friendships, marriages. Which brings us to sister Inga, a writer with a sensitive nervous system and the widow of a famous older author, Max Blaustein.

As a vengeful journalist, hot on her tail, digs up a “missing piece” from her marriage, Inga's new lover, a biographer obsessed with her dead husband, sends her into a newfound frenzy. Her teenage daughter, Sophie, is finding her way out of post-traumatic stress in the wake of 9/11 by writing poetry.

The rest of the lonely, bereft and left-behind look for answers from philosophers all and sundry: Kant, Crick, Emerson, Kierkegaard. A most fascinating lesson comes from Erik's patients, past and present, such as Ms L, who feels either angry or “frozen out”, Mr T, who takes dictation from the dead, or Mr R, who is always asking: “What do you know?” Elsewhere the hoity-toity conversations about hypnogogia and neurology might suspend our belief, but are preferable to the ventilations of grief, which tend toward the mawkish.

Yet the important point to be made is that the dead are not silent, and what they say defines the living. So as Erik makes their stories his own (to repeat, reinvent, revise, rewrite) everything gradually coheres - culminating in a glorious denouement under a snowfall - and simultaneously flutters away in multifarious directions. This novel is a masterful semi-self-portrait by turns abstract and realistic, intimate and alienating, effulgent and bleak, concise and blurry, straightforward and elusive - but the author couldn't have it any other way.

The Sorrows of an American by Siri Hustvedt
Sceptre, £16.99; 320pp
Buy the book

Times Recommends

• The Sunday Times 100 best holiday reads
• What will we be reading this summer: the booksellers predict
• Literary festivals: a survivor’s guide