Somewhere Only We Know (Nowhere Boys)

“Many philosophies, when discussing the classical elements, only refer to four (water, fire, earth and air) but in some there is a fifth element, aether. Fiona Ainsley is that fifth element. 
After being forced to spend a night in the untamed bush, alone with four other boys, after her group gets lost on their school excursion Fiona returns to Bremin to find that her parents do not remember her and her best friend classifies her as a 'freak'. What is going on in the small town of Bremin? Why can't anybody recall who the four teenagers are? And why is there a demon out to kill them?