Part 3 of the Touchstone Trilogy. Cassandra Devlin doesn't know what she's for. But she knows she's running out of time. Since Cass was rescued from the abandoned world of Muina, the Aussie teen has proven more than useful to the people of Tare. Expeditions to their home world no longer end in slaughter. The teaching city of Kalasa has been unlocked. After years of searching for answers, they are starting to make progress. But space is tearing itself apart. Ionoth attack in ever-greater numbers. And "the useful stray" has been injured so many times that the Tarens hesitate to use her for fear of losing her. With one particular Taren now her most important person, Cass is determined to contribute everything she can, and hopes to find some answers of her own. What is the link between Muina and Earth? Why are the reclusive Nurans so interested in 'rescuing' her? And what role in the crisis do the inhuman Cruzatch play? Can Cass keep herself together long enough to find out?