It is Midsummer, 1631, and while Alexander Seaton and his fellow masters enjoy the holiday, Robert Sim, librarian of Marischal College, is murdered in a dark alleyway in town. As the university and town authorities investigate the murder, Seaton is asked by the college principal to look into Sim's private life. During the course of this research, Alexander discovers a side to the librarian he could never have guessed, and personal feelings threaten to cloud his judgment and endanger his new marriage.

It is only when a second, apparently unrelated murder comes to light that Seaton begins to piece together the connections between a young weaver, a consignment of books, and a college in the Low Countries in order to unmask the perpetrator of a years'-old deception.