Astra (Gaia Chronicles)

Like every child in Is-Land, all Astra Ordott wants is to have her Security Shot, do her National Service and defend her Gaian homeland from Non-Lander "infiltrators." But when one of her Shelter mothers, the formidable Dr Hokma Blesser, tells her the shot will limit her chances of becoming a scientist and offers her an alternative, Astra agrees to her plan.
When the orphaned Lil arrives to share Astra's home, Astra is torn between jealousy and fascination. Lil's father taught her some alarming ideas about Is-Land and the world, but when she pushes Astra too far, the heartache that results goes far beyond the loss of a friend.
If she is to survive, Astra must learn to deal with devastating truths about Is-Land, Non-Land and the secret web of adult relationships that surrounds her.