An Indecent Obsession is a psychological drama set during World War II. The novel takes place in a military hospital on a South Pacific island, where Sister Honour Langtree, a dedicated Australian Army nurse, is in charge of Ward X, known as the "troppo" ward. This ward houses soldiers suffering from psychological trauma, known as battle fatigue (what we now call PTSD).

Honour has developed a deep bond with her small group of patients, who are struggling with the emotional scars of war. Their fragile world is disrupted when a new patient, Michael Wilson, arrives. He is physically fit but carries emotional wounds that challenge the balance of the ward. As relationships form and tensions rise, the novel explores themes of love, loyalty, trauma, and the fine line between sanity and madness.

The book, like McCullough’s famous The Thorn Birds, blends romance with complex human emotions, offering readers a poignant look at the impact of war on the human spirit.