Deep under Sao Miguel island, rumoured to be the last emerging part of Atlantis, Professor Mortimer has discovered samples of a mysterious radioactive metal. Could it be the Atlanteans' legendary orichalcum? When he and his friend Blake set out on an expedition into the depths to find out, sabotage occurs in the form of their old opponent Olrik. And soon, all three will be embroiled in a power struggle far bigger in scope than they could have imagined.
This is volume 12 from the series.