The Nautilus, a strange building shaped like the chambered shell of the same name, was built in South London in the early 1930s. Designed on Modernist and Utopian principles, it was a haven for a floating community of cosmopolitan refugees, intellectuals and artists. Now, at the end of the century, only two of the original inhabitants still occupy their chambers -- Celeste Zylberstein, joint architect with her late husband of the Nautilus, and Francis Campion, an elderly poet. Gus Crabb, a dealer in bric-à-brac, is the only other resident until, to the Nautilus, like a hermit crab seeking a home, comes Rowena Snow. Of Indian/Scottish parentage, orphaned, without family or friends, Rowena is in search of her own Utopia -- or the Heligoland of her childhood imagination.