[1][2][3] Taking place in an alternate history, the story follows the adventures of Dido Twite in a fictionalized version of South America.

In this world, part of South America is occupied by Ancient British (Celtic) colonists following an invasion hundreds of years before.

After her adventures in Nightbirds on Nantucket, Dido Twite is travelling back to England on the naval vessel HMS Thrush.

Travelling to Bath, the capital city, the crew learn that Ginevra wants them to help her recover a lake, which she claims has been stolen by New Cumbria's neighbour, Lyonesse.

It then transpires that Holystone is an incarnation of Arthur, who for a thousand years had lain in suspended animation on an island in the missing lake.