Down Below and the Archon's Castle

Zoe enters a Wizard of Oz-like world to find her lost friend Tod. There, she finds help in the form of a Sphere, a Rubbery Man, and a Rock Man. Their journey takes them below ground where they find Ancient Ones made of stone,  a castle ruled by a mad scientist, and a planet where no more children are being born. This  tale is the first of a seven-part series, which follows a couple throughout their lives.