The Land of the Boran - Robert a G Erickson - Bog

Effita, the caretaker of the Boran, returns to Duscany to enlist Cassy and her twin brother Lenny in the repair of the timeline. They're immediately drawn into a dastardly plot to destroy all of mankind by the enemy of time, Scorpio, the master of Hades itself.
A seeker called Effita is mistress of the Boran, the master of time itself. She tells Lenny and Cassy that the Boran was impressed by their powerful use of magic the last time they met. The Boran implores them to repair one of a series of temples, which was destroyed by an unknown enemy.
Accepting, they enlist Master Sorcerer's brother Breeden to help them. Since Breeden has only recently become human, Scapita wants him to experience the world the hard way. In order to reach the destroyed temple, they have to pass through another to reach the correct timeframe. However, the master plotter of Hades, Scorpio, has boobytrapped it with giant scorpions.
Breeden is whisked away along with Cassy and her little sister Heather into the ancient past of Greece where gods and goddesses rule for real, leaving Lenny and his girlfriend, Jenna, to repair the temple timeline on their own. Cassy, however, works her magic behind the scenes as a goddess called Kassandra, the teller of catastrophic prophecies, in order to foil Scorpio's plot to destroy all of mankind. Unless Lenny and Cassie can repair the temples and the timeline, there is no hope of a future for anyone.