This article addresses the ongoing discord among the federal courts of appeals with respect to the implications of the U.S. Sentencing Guidelines' "one-book rule" and its constitutionality under the Ex Post Facto Clause. A recent decision by the Second Circuit, United States v. Kumar, produced the most extreme position in a three-way split among the circuits by holding that the application of a single Guidelines manual to multiple offenses—even offenses predating that manual's publication—is always permissible under the Ex Post Facto Clause. The issue brings together two separate and difficult areas of jurisprudence applying the Ex Post Facto Clause: the permissibility of allowing one crime to "trigger" heightened punishments for previous crimes and the ongoing circuit split over the application of the Ex Post Facto Clause to the Sentencing Guidelines.