The story, only 4.5 pages long in paperback, tells of the exploits of Alderic, Knight of the Order of the City, to seek and purloin the fabled hoard of precious gems rumoured to be held in the castle of the Gibbelins.
These strange creatures live in a land chained to the Earth across the river ocean, and they have a built a tower at the narrowest point to attract humans, on whom they feed.
He swims the river, spends the night breaking into the supposed treasure-cellar with a mighty pickaxe, and finds the gems.
Dale Nelson has theorised that "The Hoard of the Gibbelins" was an influence on J. R. R. Tolkien's poem "The Mewlips", collected in The Adventures of Tom Bombadil.
Similarities of plot and character apart, Nelson describes story and poem as sharing a "charming quality of insincerity", as both warn of imaginary dangers.