Black Goldis the third book featuring Cyrus and Rudy's adventures on the farm, following Not for Saleand Blackberry Juice.

Cyrus and Rudy spend the last days of summer selling dahlias, blackberries and tomatoes at their roadside stand. When a neighbor drops off a bin full of red wigglers, California earthworms that break down compost into fertilizer, Rudy and Cyrus become worm moguls as they discover just how in demand the Eisenia fetidaare.