Everything in Perdido Beach seems normal.
Everyone over the age of 15 disappears and an indestructible translucent barrier blocks of the world from the 10 miles square which surround Perdido Beach.
All the kids start developing superpowers and animals mutate to create things like flying cats (nice things) and flesh eating worms (not so nice things).
An evil alien drops from outer space into a mine shaft and attempts to destroy what is left of Perdido Beach.
And a 14 and a half year old kid called Sam has to deal with all that!!!
He and his friends must fight the evil alien thing (which is called the gaiaphage / darkness) and also some kids with superpowers who have gone crazy.
There are 5 more books in the series!!!