Spyger: A thrilling adventure novel for 9 to 12 year olds

Zoe and Kirsty witness a flying saucer landing at a disused factory the day before Kirsty leaves for a new life away from the town. Later, after Kirsty has left, Zoe finds something the saucer left behind. An alien egg.

Zoe is excited about the sighting and discovery, but has no one to share the secret with, until she meets Tom who has moved into Kirsty's old house. He suggests they keep the discovery a secret. They are both afraid what the authorities might do to the alien egg.
Can they protect it?
Will it survive?
Will their secret be discovered?