Among the so-called “trial stories” (Satan processes), diffused in the Middle Age to explain the rules of procedural law, “Liber Belial”, also known as “Consolatio peccatorum”, was one of the most translated and printed books in Europe between the fifteenth and sixteenth centuries. It was written in 1382 by Jacopo da Teramo (1349–1417) who described the imaginative story about the trial in which devils decided to bring a lawsuit against Jesus Christ, when, after the Resurrection, he descended into the Hell to free the patriarchs’ souls. Satan appointed Belial as his proxy and appealed to the divin justice in order to be able to start a process against Jesus. The text is full of clues and suggestions referring to fields of theology, politics, law, literature, simbolic representations and iconography (in various printed editions the text is embellished with several pictures representing procedural phases and some scenes taken from the Bible). The lawsuit brought by Satan and devils against Jesus Christ and angels stood methaphorically for the conflict between Popes in Avignon and those in Rome. In this way the text indicated a legal path as a mean to ensure that the good would defeat the evil, what means that the Roman Court would prevail. In "Liber Belial", the author has shown his knowledge, on subjects of theology and law. One can regard it as Janus with two faces: a theological side, with a considerable number of quotations taken from the Bible, and a juridical side that focused on two trials, i.e. the first instance one, and the second instance one (with a digression about arbitration). The latter seems to be a veritable Guidebook for judges, lawyers, litigants and students, accurately provided with references to legal sources. "Consolatio peccatorum" presents interesting juridical content. It is enough to say that 249 references (almost 1/3) for total 844 citations, relate to Canon Law sources (Decretum by Gratian, Liber extra by Gregory IX, Liber sextus by Boniface VIII, and Clementinae) and Roman law sources (Codex, Digesta, Istitutiones and Authenticum). The work describes the complex and obscure procedural mechanisms, unraveling their secrets into the vast profane world in a fictionalized style. In "Liber Belial" one can see the interplay between theology and law, cleverly interwoven with a clear aim to offering the reader a lucid presentation of civil proceedings in all their phases.