Singing the Dogstar blues

Seventeen-year-old Joss is a rebel, and a student of time travel at the prestigious Centre for Neo-Historical Studies. This year, for the first time, the Centre has an alien student: Mavkel, from the planet Choria, who has somehow survived the usually fatal loss of his linked partner Kelmav. And Mavkel has chosen Joss, of all people, as his roommate and study partner. She gradually realises that she is expected to link with him, as she is the most open of all the students. Then Mavkel gets sick. Joss quickly realizes that his will to live is draining away. The only way she can help Mavkel is by breaking the Centre's strictest rules - and that means going back in time to change history.