In the third Mud novel the kindly fish discovers to his dismay that the other animals have been infected with a virus that destroys their altruism and makes them greedy and selfish and thoughtless of their fellows. This cannot continue, and Mud has to embark on a perilous adventure to Nothing Atoll to find the Shadow-Keeper in order to procure a shake of shock-shade, a glowing jungle fern that opens only at midnight. Marjorie the wave tells him he has to take with him Fishmeal, the paragraph duck who studied under the great Queequack and who holds the secret of organization.
At the last minute they are joined by Baldwin the beetle on a raft that takes them across a bioluminescent sea to the atoll. They meet strange creatures called aye-ayes who help them and even suggest that they might like to stay on Nothing Atoll with nothing to do but live a long pleasant life of comfort. But Mud remembers his friends and their mission to save them from the virus. A plan is formed to acquire the shock-shade from the snapping beast that is its guardian. The friends win through in the end and Mud reflects on his adventures, the various ethical concerns raised, the sights he has seen, and the meaning of friendship.