 A year later, Keene and astrophysicist Solomon Nestor are on board the "Limbo", conducting a survey of cosmic radiation in the outer reaches of the Solar System for the Smithsonian Institution.When one of the "Limbo's" stern jets melts, they are forced to land on Pluto, in the hope of finding some refractory metal to build a new jet.Shortly afterwards, they are captured and taken to the secret lair of the pirates.