In the spring of 1662, the town of Haddington became the site of a volatile legal unfolding following the testimonies of a young resident named James Welch. Though Welch was considered too young to stand trial himself and was consequently held in custody, his declarations were treated with significant gravity by the local authorities. Among the many individuals named in his denunciations was the wife of William Finlasoun. As a married woman residing in Haddington, Finlasoun was swept into the widening net of a legal process that drew its legitimacy from the young informer's detailed confessions.
The formal proceedings against Finlasoun, recorded under case file C/EGD/506 and trial reference T/LA/1343, took place on 17 April 1662. The records identify her primarily through her marital connection to William, reflecting the period's social structures which frequently tethered a woman’s legal identity to her husband. Despite the age of the primary accuser, the authorities of the time deemed the testimony sufficient to warrant the documentation of Finlasoun as a participant in the broader series of denunciations that characterized the judicial climate of that year.