In this book, the humans meet their first aliens, the friendly reptilian Ringulian people. Next come the Kalesians, willing to share their space technology with the humans. The Ringulians live on Jupiter's ice moon 'Europa'. The Kalesians live on the planetoid, rocky world of 'Pluto'. The humans then hear from the Gloshans. They are sinister, brutal space pirates, who decide to wage a space war against the Earth people, the Ringulians and Kalesians...