Stuart Garfield finds himself alone in the Haitian jungle when his father disappears amid mysterious Voodoo rites and international unrest. Refusing to panic, Stuart studies his father's papers and discovers a dangerous plot against the United States orchestrated by the Cuban conspirator Manuel Polliovo and the Haitian general Cesar Leborge. Determined to shadow the conspirators and locate his father, Stuart stains his skin with a native root to disguise himself as a local boy and travels toward the historic Citadel of La Ferrière.
His journey leads him through treacherous swamps and mountain passes where he encounters native superstitions and encounters the elusive Englishman Guy Cecil. Stuart gains access to the heavily guarded citadel by posing as a horse-boy, eventually hiding within a ruined wall to overhear a secret conference among the conspirators. He learns of a dangerous scheme involving the Mole St. Nicholas and a potential attack on American authority, narrowly escaping peril with Cecil's unorthodox assistance using a parachute.
Leaving Haiti, Stuart travels through Cuba and witnesses local struggles and political unrest before reaching Jamaica and Martinique. Throughout his travels, he encounters various historical echoes of the Caribbean, including stories of notorious buccaneers, the dramatic eruption of Mont Pelée, and deep-seated social dynamics. These adventures test his courage and sharpen his resourcefulness as a young investigator.
The final confrontation takes place at the Mole St. Nicholas where Stuart arrives with a Jamaican preacher in a small motor boat. Trapped by Manuel and Leborge, Stuart faces imminent danger until an American marine force, led by his rescued father and supported by Cecil, arrives to arrest the conspirators. The plot is thwarted, restoring safety and demonstrating the enduring strength of international cooperation.
