Smitty sees a house explode, and grabs a suspicious character and takes him to Mac's drugstore.
Drugged and hypnotized, the man reveals that a small, peanut-shaped bomb was used in a plot to get 5 clay bricks originally from southern Mexico.
The bricks are archeological artifacts found by Professor Archer Gray, distributed among some of the expedition members for safekeeping.
Gray's daughter, Nellie, is slow to trust Benson, but helps the trio pursue the criminals.
The bricks each contain a segment of a golden belt inscribed with directions to huge Aztec treasure.