Shart of Atlantis is a seabird-riding merman from a lost race that shrank and vanished 3000 years ago. In this wry but dark Christian legend science fiction, he flies half an ocean to Rockall, to find the strange Singer whose mystic Song rules even the waves. There he and David, a naval pilot from a mind-controlled computer world nearly kill each other. Shart flies back to his undersea city with a dreadful command from the Singer. Yet what new twin perils has his proud sister Vanarn awoken in his absence? Could the terrible Leviathan really return? Meanwhile, David finds none who avoid the power of the all-seeing 'frame' except the strange Themers, who have been joined by Mairi, David's fiery Gaelic wife. David mocks her; but finds she disbelieves him too. The strange Commander Spenser sends him to find Shart again; but who hunts Spenser? Will the Lords of Atlantis condemn David? Or will war take all back to Rockall? And what does connect the Theme and the eternal Song?