Burning For Revenge by John MarsdenBook 5 of the Tomorrow Series. I really need to find books 2, 3, 4 and 6. Ellie and her surviving friends are hanging on. By chance they get the chance to inflict a major blow to the enemy. But afterwards they have to run. But where can they run to when their country has been colonized by the invaders?
This is a good prolonged chance but the nationality of the invaders has still not been mentioned. There is an apparent continuity error when Ellie mentions Lee played violin in the school orchestra, but he played piano.