Set almost a decade after Rainbow Valley, Europe is on the brink of the First World War, and Anne's youngest daughter Rilla is an irrepressible 14-year-old, excited about her first adult party and heedless of the chaos that the Western world is entering. Her parents worry because Rilla seems not to have any serious plans for her life, and is more concerned with having fun. It is revealed Marilla died between 'Rainbow Valley' and this book.
Once the Continent descends into war, her brothers and the Meredith boys promptly enlist. This upsets Anne, Nan, and Faith. With her sisters at college, Rilla is left anxiously alone at home. As the war drags on, Rilla matures, organizing the Junior Red Cross society in her village.
While collecting donations, she comes across a house where a woman has just died in childbirth and her husband is away at war. Rilla takes the sickly little boy back to Ingleside in a soup tureen, naming him "James Kitchener Anderson" after his father and Herbert Kitchener, British Secretary of State for War. Rilla's father Gilbert Blythe challenges her to raise the war orphan, and although she doesn't like babies at all, she rises to the occasion.
Along with the rest of her family, Rilla deals with the spread of the war and the death of millions, as well as her eldest brother Jem's disappearance. Meanwhile, the boy she is in love with, Kenneth Ford, begins to court her, but leaves to fight as soon as an old injury heals, leaving an even more anxious and depressed Rilla to wait at home. Susan and her cousin Sophia have important roles in this book.
At the end of the volume, the Glen St. Mary boys, excluding her dearest poetical brother, come home from the war, full of scars and permanent handicaps. Walter, the dreamiest of the children, dies in war. (This was foreshadowed in the earlier book Anne of Ingleside). His last letter is included in the chapter "And So, Goodnight". Life begins to return to normal.
Mary Vance and Miller Douglas get married, with Miller deciding to follow a career in Mr. Flagg's store after losing a leg in the war. Jem is engaged to his sweetheart Faith Meredith, and goes to Kingsport to finish studying medicine and become a surgeon. Jerry Meredith becomes engaged to Rilla's sister Nan and goes to Kingsport to finish college and pursue his career as a lawyer. Faith and Nan decide to teach at nearby schools while waiting for the boys, along with Rilla's other sister Diana. Carl Meredith and Shirley Blythe also leave for Redmond with Una, who is going to take a Household Science course to begin a career.
Kenneth proposes to Rilla with a romantic "Is it Rilla-my-Rilla?" -- to which Rilla lisps, "Yeth."
