Artie, an impressionable young pig, and Merlin, a bat, explore the world of mammals and the meaning of friendship. Through gentle humor and engaging dialogue, topics such as hibernation, camouflage, echolocation, scientific and common names, predation, and mammalian defense mechanisms are introduced and explained simply but accurately. Artie learns what pigs and bats have in common and how they differ. In a nighttime adventure, the two friends study how a flying squirrel flies and what a star-nosed mole has on its nose. Artie discovers that, although he is a slower swimmer than a beaver, he is a faster runner. When Merlin disappears to hibernate, the lonely pig makes a new friend, a prickly porcupine. Handsome black-and-white illustrations depict Artie, Merlin, and the other mammals, including a family of opossums, a bloodhound, skunk, and white-tailed deer. The book also provides additional information about bats, pigs, classification of mammals, and related topics.