Robert and Katherine love their dog, Darling, even though she has a tendency to run away and get in trouble in the village. Their father is off fighting in the war, and signs the family up to donate Darling to the war effort. The children area devastated but brave, and leave a note on Darling's collar that she should be sent back to them. Darling ends up under the care of Sergeant Hanson, who has a soft spot for the vivacious but sometimes naughty dog. Darling doesn't do well at carrying messages but has a knack for locating wounded soldiers, so is sent to the front as a Mercy Dog. During a particularly heated battle, Darling manages to save many soldiers in her squad, but sustains grave injuries. Most injured dogs are put down, but Sergeant Hanson alerts a newspaper man who publishes a story about Darling's bravery and manages to get her sent back to England with Private Kent.

Aside from the fairly new Soldier Dog by Sam Angus, there is little about dogs during The Great War. This book is part of a series entitled Dog Chronicles, and would be especially interesting to elementary students who love to read about dogs. While Darling is injured, the book is not overly gory and ends on a hopeful note.