The story begins in Kennituck Falls, as Peter and Broxholm evade those who are trying to capture the alien, quickly reaching Broxholm's ship and leaving the Earth. They swiftly travel to the far side of the Moon and rendezvous with the starship New Jersey (so named because the ship is the same size as New Jersey). Once on board, Peter is subjected to some rather unsettling albeit benign boarding procedures and finds himself in a truly alien world, on a starship crewed by aliens from various worlds throughout the galaxy. Peter is introduced to the alien Hoo-Lan who undertakes to serve as Peter's teacher to introduce Peter to the intergalactic society he has joined. Hoo-Lan can glow in the dark, giving the book its title, although this doesn't become a plot point (making this the only book in the series where the title isn't a plot point).