Tayopa! - Allen, Henry Wilson, 1912-1991 (New York : Pocket Books, 1970)
Caught in their motorboat the Sleuth by a sudden storm at sea, Frank and Joe Hardy are relieved to see the lights of a yacht. But their SOS ignored. The shrill sound of a siren fills the night air and moments later a helicopter drops an object alongside the Sleuth: a wallet containing two thousand dollars! The next day, a truck carrying a shipment of high-powered rifles has been stolen.
Keywords: Treasure troves -- Mexico -- Fiction; Mexico -- Fiction; Adventure stories