Astro the Alien sees his friends Ben and Eva playing with toy marsupials. They go to the zoo to learn more and encounter an exhibit about the Tasmanian tiger, an extinct meat-eating marsupial. This introduction to extinct animals includes a note to caregivers with additional resources, reading activities, and a word list.

If an animal could dream, what shape would its nightmare take? Would it be furry, or scaly, or drooly? Or would it be mysteriously devoid of any form? In this picture book, adapted from the Italian original, animals' nightmares take literal shape, yet the scariest place of all is the Island of Shadows, the domain of extinct creatures whose dreams have disappeared. As the "doctor of nightmares" chillingly explains to the Tasmanian tiger, "once you are gone, there is no coming back."