The Hork-Bajir Chronicles
The book is introduced by Tobias , who flies to the valley of the free Hork-Bajir , where Jara Hamee tells him the story of how the Yeerks enslaved the Hork-Bajir , and how Aldrea , an Andalite , and her companion , Dak Hamee , a Hork-Bajir , tried to save their world from the invasion . 
<triplet> Andalite <subj> Tobias <obj> part of the series <subj> Yeerks <obj> part of the series <subj> Aldrea <obj> part of the series