13 Square: This is the thirteenth book in the series.
Take a long look at that cover, because that's one of the least offensive things about the text of this book.
The Hardy Boys have taken their beloved power boat out for a cruise when a dusky foreigner comes speeding out of the fog, hits them, and keeps going. Some quick action on the boys' part saves their lives and limits the damage done to the boat, but such actions are hardly those of a gentleman.
Determined to get satisfaction, the boys inquire after the boat and discover that it was a rental and the man is unknown in town. Disappointed, the boys go where the action is in Bayport: the city courthouse, to see the ongoing trial of the company that had been selling fraudulent stock in Mexican oil.
The place is packed, of course, and the boys arrive in time to hear the case being delayed because a star witness has gone missing. They also see the dark foreign man! In tracking him, the boys discover his link with the fake oil stocks, his gifting of sickly hairless dogs, and his penchant for carving his sigil on doors. As a reward for their sleuthing, their father takes them along on the search for the missing witness and they end up in Mexico.
This was a difficult one to read. The book relies on the trope that the only good foreigner (Mexicans in Mexico are foreigners, fyi) is a rich one and the only good Native Americans are full-blooded strong and silent types. A lot of disdain is given to the "half-breeds" that live in hovels and caves.
The only reason this gets a full star at all is that after the boys are captured by a gang and mistreated by those cads and Frank and Joe's bluster is met with laughter. They ask their Indian guide what will happen to them out in this desert (where nobody knows where they are).
Which, yes. Finally. Thank you, realism.
There was very little else to redeem this book. I imagine the 1960s rewrite scrapped the lot.
Next: 'The Hidden Harbor Mystery'
Previous: 'Footprints Under the Window'