High atop a hillside on the Greek island of Corfu overlooking the Ionian sea sits the Old Fortress, an ancient ruin built to keep out invaders. Leonidas, a highly protective and dedicated dog, guides tourists through the graveled pathways with a keen alertness for their safety. Like the Greek soldier he is named for, Leonidas thinks of others as he guards them from danger. Leonidas' bravery and loyalty have earned him the reputation of being The Old Fortress Dog.

When his master's grandson, Nikos, comes from America to visit, Leo senses the boy's sadness. Determined to bring a smile to the boy's face and laughter to his voice, Leo doesn't leave his side, even though once, it meant disobeying his master.
Being the Old Fortress Dog can be perilous at times, but Leonidas is alert and strong for the task. With Leo by his side, Nikos soon discovers his connection to the Old Fortress. Like a good soldier, Leonidas perseveres in his quest...to hear the boy's laughter.
Will Leonidas discover why Nikos is sad. Can he use his instincts and kind heart to gain Nikos' trust and understanding?