The Mark on the Door

Frank and Joe Hardy, after being tipped off by their father, international detective Fenton Hardy, follow a trail of clues that lead them to Mexico. They must solve the mystery behind the mark on a particular door to thwart an international plot. In their motorboat, the brothers navigate through various challenges and adventures to uncover the truth and protect national security. In their motorboat the Sleuth, Frank and Joe Hardy search Barmet Bay for a dangerous stranger who has stolen a valuable boat. Suddenly, in the eerie fog, they spot the craft drifting aimlessly out to sea. What happens next starts the young detectives and their pal Chet Morton on an intriguing adventure that takes them to Mexico and into the comparatively unexplored desert and mountain regions of Baja California.