Hemlock at Vespers is a collection of shot stories featuring Sister Fidelma. It is listed as the 9th book in the series, but the stories cover a range of her history. All of them are without her partner, Eadulf.
I felt there wasn’t enough character development, so being familiar with the character of Sister Fidelma is valuable, but not critical. Another shortcoming is that every story has to repeat some of the basic information, such as that she is a high-ranking member of the court and has certain rights. Despite those shortcomings, the mysteries are good and Peter Tremayne tells the stories well.