This chapter reconstructs the demise of the Catholic utopia of “revolution” that dated back to Europe’s fin-de-siècle. This is a story of how Stalinism teased out and laid bare the exclusionary, integralist elements that had been part and parcel of Catholic “revolution” from the start. For the Catholic socialists of Dziś i Jutro (renamed PAX in 1952), the Stalinist years were, paradoxically, a moment of unparalleled possibility. While their countrymen languished in prisons or hid in forests, Poland’s Catholic socialists had the opportunity—with the support of Western European allies like Esprit’s Jean-Marie Domenach—to propose new avenues for engagement in public life. In the end, however, the 1954 publication of Bolesław Piasecki’s magnum opus Essential Questions met with condemnation from the Holy Office; his movement’s allies abroad, too, were on the defensive against Rome. At the same time, PAX’s postwar generation, led by Tadeusz Mazowiecki, broke dramatically with Stalinism. Integralism’s avatars—anti-Semitism and anti-Germanism—had guided transnational Catholic “revolution” away from Aquinas and toward Marx. In the end, PAX’s run as the definitive laboratory of Catholic “revolution” had ended, leaving integralism and heresy.