In Santo Domingo, a Mr Hendrix asks the experienced skipper Cournot to look over the “Dragoon”, a ketch being sold by a widow in New York called Mrs Osborne.

She wants to find her stolen vessel and Cournot suggests a seaplane pilot in Kingston, Jamaica, who flies the two in search of where the “Dragoon” was last reported.

On going aboard, Cournot and Mrs Osborne are taken captive by a vicious gun runner called Morrison who with his gang is already holding Hendrix and has overloaded the “Dragoon” with weapons and ammunition for delivery to Central America.

Morrison makes Cournot do the exhausting work of ferrying the heavy cases one by one to the sandbank, aiming to refloat the vessel and then reload it.

Disputes among the crooks lead to Morrison being left alone on the sandbank with all the hardware while Cournot, Mrs Osborne and a wounded Hendrix are on the boat.