Shortly before Christmas, Professor James Lowell is found brutally attacked in his rooms at Walsingham College, where Anna Hopkins works as an administrator. Baffled as to why anyone would wish to harm such a gentle, scholarly man, Anna discovers that Lowell had a connection with her fellow dogwalker, Isadora Salzman, who knew him as an undergraduate in the 1960s, a co-member of the so-called Oxford Six. It turns out that Isadora has been keeping a surprising secret all these years. But someone else knows about Isadora's secret: someone who has sent her a threatening, frightening letter. Could the attack on Professor Lowell have its roots in a 50-year-old murder? And who is targeting Isadora and the surviving members of the Oxford Six? Anna, Isadora and Tansy, the dogwalking detectives, make it their business to find out.