Another message, one they hoped never to receive, the single word "Grun" sends Jack Coughlin, his brother, Collin, and their friend, Danny, back to The Hidden Moon and a fight for their lives!

Jack Coughlin's magical stone from Anron sends another Morse Code message. This time the dots and dashes spell G-R-U-N, the name of the evil creature they all thought was dead. Jack, his brother, Collin, and their friend, Danny, return to outer space to help their Anronite friends, Karna and Nidar. Grun, the enemy of the People of Light, is very much alive and is determined to rule The Hidden Moon for his own. The battles to save Anron from Grun's control take the boys from the dark side of the moon to the dangerous Bogg on nearby Planet IXX where they must risk their lives to win the freedom to go back home again.

Be sure to read the other books in the series: The Hidden Moon and Return to the Hidden Moon, where more adventures await the boys and their two new moon friends, Nidar and Karna.