The Mark on the Door (Hardy Boys, Book 13)
In their motorboat the sleuths 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. The search for the meaning behind a mysterious symbol that terrorizes the people of an entire village, a daring escape from a submarine, perilous encounters with the band of renegade Indians, and unusual smuggling operation -- all combined to make this one of the Hardy's most exciting cases. - Flyleaf.