The experimental British airship D100 has disappeared, believed lost with all hands. But when mysterious reports reach London in 1929 that it has been seen, the Air Ministry needs to send someone to British Guyana. Someone brave, resourceful and expendable like Captain John Caspasian of the Twelfth Gurkhas.

Soon Caspasian is on board the lost airship's luxurious sister-vessel, floating over the Atlantic clouds in the company of the rich and adventurous, among them a beautiful Hollywood starlet. But also on board is a ruthless saboteur. And waiting in the wings is Caspasian's old enemy Brigadier Percival.

Before long, Caspasian will have to summon up all his cunning and endurance to rescue his fellow passengers.