Books in the Harold and Clara series

Hey, you! (Reading the description of this book) Is this your first Harold and Clara? Wow, you're in for a real treat! Evil aliens, secret missions, and an underground base on the moon. Sound interesting?How about space battles, mysteries of the universe to solve, and of course, a sassy cat and brave dog?A mysterious request to join a top-secret group: The Planetary Exploration Team (or P.E.T for short). Its mission: to save the Earth ... from aliens!Are you brave enough to join our heroes, Harold and Clara, and help them save the world from the horrible Gygans?