Capt. Alfonso Payton, the Sky Pirate, kidnaps Helen Grayman, New York's richest girl, and carries her away in his airship, the ''Chameleon''. He poses as Commodore Brown.
She thinks her abduction is a practical joke. Payton takes her to his lodge in a Labrador wilderness. William Grayman, her father, secretly summons the police.
By wireless telephone Payton demands $10,000,000 ransom from Grayman, who agrees to meet him at Tribes Hill with the money. Grayman plans to trap the pirate.
Helen and her maid are well cared for by Payton, but are closely guarded by Indian John. Helen suspects that they are prisoners.
One after another Payton captures four police aeroplanes sent to trap him and kills several policemen before Grayman reaches the scene.
Grayman and police commissioner Braman reach Tribes Hill. Payton kidnaps Grayman, who again promises to pay the ransom.
Payton takes Grayman home. Helen receives a forged letter from her father, which reassures her. She replies to her father's letter.
Grayman fears Helen will fall in love with Payton. Secretary Grantham offers government aid and assigns Lieut. Allan the task of locating Payton's lodge.
This Allan does by receiving wireless messages from Payton at New York and Buffalo with the aid of geometry and his new invention.
Allan, Grayman and Grantham start for Payton's lodge with five war aeroplanes. Helen, learning that she has been kidnapped, escapes, but is captured.
Allan's war aeroplanes reach Payton's lodge. The ''Chameleon'' fires on them, disabling Allan's favorite aeroplane, the ''Eagle''.
Payton escapes with Helen and her maid in the ''Chameleon'', pursued by Allan's ''Osprey'' and ''Skylark''. Allan fires at the ''Chameleon''.
Payton cripples the ''Skylark'' and dodges from cloud to cloud in desperate efforts to escape from Allan's ''Osprey''.
The ''Osprey'' cripples the ''Chameleon''. Payton and Helen drop to the ground in parachutes. Allan goes to Helen's rescue, defending her against Payton's attacks.