We return to Aldebaran, the planet where the first human colony in the solar system was founded. Mark and Kim, teenagers whose village was annihilated, have met a woman named Alexia during their escape. She is a biologist and a friend of Driss, the man who knows a lot about the catastrophe. Alexia shares Driss's secrets. The government is very interested in her and sends soldiers to pursue her. While trying to help her, Mark is arrested and languishes in prison for 3 years. It's the mysterious Mr. Pad, an odd character Mark has already met, who helps him escape from prison....

This two-volume book includes The Expedition. The Survivors: Mark and Kim are sent to Betelgeuse to look for survivors of the spacecraft crash that killed 3,000 people seven years earlier. Two survivors tell them the colonisers had been divided over whether the indigenous creatures called Lums are as intelligent as humans. If they are, the humans would have been forced by law to abandon their colonising enterprise. Kim decides to investigate for herself. The Expedition: Kim and her team have gone off into Betelgeuse's deepest canyons to investigate Logan and Menegaz's claims. They discover that danger can come from the most unexpected sources....