The Cave of Dreaming — Margaret Pearce

Mike and Alinea and their alien pet, Beeper, are expected to stay out of trouble during their holiday on an archeological dig somewhere in Central Australia.

It is not their fault that they trigger a time gate in the cave of the dreaming. They have to escape being lodged in an intergalactic lost property office until claimed, avoid being eaten by the deadly Kloog who are raiding the protected planets again, and help their new friends before they find their way home again.