“Under the Mountain” by Maurice Gee
Maurice Gee is one of New Zealand's best-known writers, for both adults and children.
Twins, Rachel and Theo, visit Auckland and meet a strange old man and a couple of freaky neighbours.
The red-headed twins discover that they are a crucial part in the war between two alien races.
and only they can save their world from destruction by huge, powerful alien creatures.
This is a fun book, and I'd recommend it to people of all ages.
I have heard that the movie can be very scary...