The Pit series and the book Pit's Letter describe the journeys taken both together and separately by a boy and his dog. The boy grows up to be a biology student and a scientist; he and the dog are unwillingly parted; they will meet again, but only after the dog has become a laboratory subject and the scientist has been fatally infected with a "hot" virus. The cycle depicted in Pit's Letter pays homage to William Hogarth's "The Four Stages of Cruelty (1751)," a series of engravings that were made, in Hogarth's words, "in the hope of, in some degree, correcting the barbarous treatment of animals, the very sight of which renders the streets of our metropolis so distressing to every feeling mind."