Six-year old runaway Peter Pendleton comes across Martin's spaceship in the woods while Martin and Tim are off away doing other work for Martin's test flight. Peter actually manages to take a flight on the ship, but after Peter returns home, his family and officials believe his is just a story of fancy. That may change as Peter has taken Martin's Electro-Magnetic Neutron Converting Gravitator, on Earth an anti-gravity device. Martin has to get it back from Peter before nosy reporter Grinnell, who is already suspicious due to some coincidences, gets the truth and the device from Peter.
—Huggo