Sammy is a football crazy rescue puppy. Mouser is a fearless grey tabby. Together they make an unlikely pair that won't be parted, not even by the First World War. As the war rages in Europe, Londoners are sending brave animals to help the soldiers - and Mouser and Sammy are soon on their way to the trenches. Boldly criss-crossing no-man's land they make new friends of every nationality - and reunite with old ones. But on the muddy front line, under fire and constantly in danger, will their friendship be enough to save them so they can return home together?