Book 1

Alien Alert!

by Debra Hess and Carol Newson

Published 1 January 1900
Seeing a spaceship land near her house and meeting one of its occupants, an alien boy her own age, eleven-year-old Super Spy Cassie Williams helps him disguise himself as an earthling and look for his missing robot.

Book 2

Too Many Spies

by Debra Hess and Carol Newson

Published 1 January 1900
Zeke, an alien boy stranded on Earth, continues to pose as a human with the aid of eleven-year-old Super Spy Cassie Williams, while trying to discover the identity of the man in black who is following him. Sequel to "Alien Alert."

Book 3

Escape from Earth

by Debra Hess and Carol Newsom

Published 1 May 1994
Cassie and her friend Zeke, a boy from outer space, try to uncover the meaning behind a mysterious message left on board his ship, while dealing with the suspicions of Ben the class bully.

Book 4

Spies, Incorporated

by Debra Hess

Published 1 May 1994
When Hillsdale's pets begin to disappear, it is up to eleven-year-old Cassie, her classmate Ben, and Zeke, a boy from outer space, to figure out what is happening to them.