This article was published in a special issue of Past & Present dedicated to the relationship between global history and microhistory. It examines in detail a ‘hard case’ between two Corsican merchants, Pietro vs. Franchi, which hinged on two interrelated questions: is it true that a master inherits his slave’s (mamluk) outstanding credits in Ottoman North Africa? And, if this is the case, can this debt rightfully be reclaimed on ‘Christian land’ (to borrow the terms used in the legal documents themselves)? This essay tries to apprehend the transformation of disputes and claims in different legal arenas, regions, states, and political entities. This approach unveils the complex web of jurisdictions in which social actors of the early modern period could navigate. The Pietro vs. Franchi dispute was indeed a ‘multi-sited’ trial on a transregional scale, which circulated from Tunis in 1619 to Pisa in 1625, through different procedural stages in Corsica, Genoa, and Tuscany. Instead of comparing a priori different legal institutions across the Mediterranean, with the risk of brutal and anachronistic analogy, following in detail disputes in multiple jurisdictions helps to capture the same legal questions in different locations and contexts. The first part of the article reconstructs the backgrounds of the three main actors of the trial: the bey of Tunis, Murād Bey, his nephew, the Corsican Anton Marco Pietro, and a second merchant, Simone Francesco Franchi. Their biographies shed light on the family ties and protection networks of Corsican merchants that criss-crossed the Mediterranean between the Ottoman province of Tunis, Cap Corse, and the Tuscan port of Livorno at the turn of the 17th century. The second part of the article analyses the roles played by written documents and oral evidence in different jurisdictions. It retraces the case as it moved through different magistracies, from Tunis to Pisa, with a particular focus on the difficult enforcement of sentences, which led to lengthy trials. The third part of the article focuses on the uses of the law by litigants, who did not hesitate to express their anger and open hostility to each other during their appearances. The personal animosity between litigants reveals deeper mechanisms of political, economic, and diplomatic intimidation that were designed to influence judges. The final section of the article focuses on the translation and application of Islamic rules of succession as they were practiced in a Christian country. It highlights the role of witnesses, merchant practices (the so-called pareri) and customs, but also the use of the lexicon of religious antagonism as means of harming the opposing party in litigation. The article draws on a wide variety of sources, including civil court records, parish registers, diplomatic correspondence, and Inquisition trials. Investigated in all its complexity, the ‘hard case’ allows us to articulate together the social, emotional, and institutional history of law, and the technical and intellectual dimensions of legal operations and categories, two aspects that historiography often tends to study separately.