The Daughters of Mars, By Thomas Keneally

A triumphant novel about sibling rivalry, pain, guilt, self-esteem and the horrors of nursing the casualties of conflict

The opening chapter of The Daughters of Mars is baldly titled "Murdering Mrs Durance". Within the first four pages, Mrs Durance, a farmer's wife conditioned to a life of toil and now raving with the agony of inoperable, post-metastasis cervical cancer, passes away. Sally, the younger Durance daughter, had gradually amassed a reserve of morphine from her day job in the Macleay District Hospital in rural New South Wales. Naomi, the older, more aloof and self-determined sister who had fled the homestead to nurse in Sydney, returned on the night of Mrs Durance's death and, it would appear, happened upon Sally's stash.

The details are delicately opaque in this quietly dramatic overture, but the quickly sketched encounter neatly introduces Thomas Keneally's principle themes: overwhelming pain, and the morality of its relief; the equally destructive effects of illness and deliberate violence to the body; the caustic interplay between guilt and self-esteem; and the passionate push and pull of the evolving relationship between the two Durance sisters.

Temperamentally very different, the sisters have a prickly relationship that forms the narrative spine of this substantial saga. Beyond plot mechanics, however, they also operate as the novel's emotional nervous system, particularly in Sally's self-critical zeal to analyse, to feel, to engage fully and dutifully in the horrors of the world.

Those horrors quickly materialise in the form of the First World War. With Mrs Durance safely interred, Sally hops to Sydney where both sisters volunteer as war nurses, taking ship for Egypt before being posted to the Archimedes, a hospital ship receiving the freshly mutilated from the 1915 Dardanelles campaign on the Gallipoli peninsula. Keneally draws in the engaging clique that jostles around the Durance girls: the cheery Irish lass Slattery; Freud, fiercely independent but able to sing to the wounded in theatre; Carradine, who is secretly married. The forceful personality of Matron Mitchie keeps her women sane and effective in hellish conditions, while Sergeant Kiernan, a medical orderly whose Quaker beliefs prevent his taking up arms, provides wit, good sense and replenishing moments of sober wisdom.

Bodies, mostly still living, arrive in waves. Keneally skilfully allows the wearying monotony of dismemberment and death to wash over and permeate his characters, dazing and disorienting them, conditioning their responses, submerging their sense of normality. The Daughters of Mars is a long novel, and one of its triumphs is the relentless description of the war-wounded. Dialogue, incident and character provide plenty of interest, but the persistence of the material accumulates into a sense of the true enormity of nurses' front-line service, in some ways made all the more gruesome for the lack of any first-hand conflict. The offstage battle is tallied in lost limbs, gangrene, shattered skulls or loops of intestine, compounded, once the theatre moves to the Somme, by gas attacks, shell shock and influenza.

At times, Naomi is quietly but not mutinously outspoken about the incompetence of the generals governing military and medical strategy; but there's no undertow of redemption or moralising in The Daughters of Mars. Keneally more readily offers a perplexed long look at the panorama of agony, and a close observation of the moral resilience of his characters under duress.

This is familiar terrain: all of Keneally's recent novels are preoccupied with profound ethical dilemmas amplified by military stresses. Revolutionary fervour stoked The People's Train while The Tyrant's Novel mapped the queasy slide from integrity into complicity with an oppressive regime. The Office of Innocence explored spiritual leadership under war conditions and The Widow and Her Hero probed the nature of moral courage. In more ways than one, his latest novel has resonances of Bettany's Book, Keneally's masterful 2007 novel in which two sisters – one aloof, one dynamic – find their relationship tempered by conflict zones.

Bettany's Book took on some of the big questions in a framework of family relationships. In The Daughters of Mars, the Durance girls are diligent, peripatetic actors on a wider landscape of pain, but neither seems able, as is shrewdly remarked of one chirpy veteran, to possess "the gift of contentment". There's a restlessness to their demeanours, and an unacknowledged fascination for, almost an addiction to, the sheer incomprehensible horror of the war, as though its terrors filled a need in their souls.

Keneally provides two alternative endings, which offer contrary outcomes for his protagonists. More than anything, this reinforces the sense of the arbitrariness of life that gives The Daughters of Mars its underlying bleakness. Whether it's the injustice of Mrs Durance's diligent toil truncated by the eviscerating pain of cancer, or the hazards of war suddenly crushing the prospect of love, or joy, or fulfilment for the most selfless of nurses – the outcome, Keneally seems to suggest, is not necessarily uplifting.