The Undersea Kingdom — Tim Murari

Having discovered the first part of the key that will send the evil kingdom of Gondwana back down to the bottom of the sea, our six teenagers now have to find the other five parts. Who has them and where, and in which time and space? The clues are in their medallions which they must decipher. The evil empress Cremelle is in pursuit to stop them. Why is she afraid of Axxiss, the boy leading them? Who is the mysterious black dog which protects and guides them? Who created the excat clones of the teenagers which are determined to kill them? Who has started the revolution in the undersea kingdom?
The six, growing closer to each other, have to survive the many dangers to find the secrets of this strange key.