Orbianna: The City Beneath the Sea

What is the strange formation on the Atlantic sea-bed?
Could this be the fabled Atlantis?
Is it an ancient Orbiane city, flooded after the end of the last ice-age?

Following Mary and Si's previous experience, they investigate discoveries from the mid-Atlantic to Egypt.
There they find more questions;
Did the Egyptians build the Giza pyramids?
How did they carve and move the massive stones?
Their discoveries challenge our accepted view of human pre-history.

But they are not the only ones interested in these discoveries.
While searching for the truth, they have to ensure these discoveries don't fall into the wrong hands.