FORT WORTH — There we were at an original instruments concert when, suddenly, a contemporary music showcase broke out.Texas Camerata, an early music ensemble that (usually) performs on instruments matching the era of the music being played, opened its 24th season with a performance at St. Patrick’s Cathedral on Sunday night that offered something never heard at the group’s events — modern compositions. The concert, titled “Portraits of Mary,” offered several works inspired by the Blessed Virgin. But most of the pieces on the tidy, one-hour program were sections from British composer Henry Purcell’s Fairy Queen, which was based on Shakespeare, not the Bible. And the concert opened with a wonderful brass-driven fanfare by Purcell from Arise My Muse, which was written for the birthday of Queen Mary.Between those instrumental sections were vocal works by a couple of obscure, early Baroque-era composers (Krieger and Marini) and one Holy Roman Emperor, Leopold I.Most of these works were chosen to highlight the talents of guest artist Ryland Angel, a countertenor who has performed frequently with Texas Camerata and similar groups in this country and abroad over a career spanning more than 30 years. And the pieces did their job well. They showed Angel’s unworldly, crystalline voice to be as riveting as ever.And to allow the audience to enjoy Angel’s unique vocals in a slightly different context, two contemporary works were included, Laude Novella by James Kennerley and O Clarissima Mater by Julian Wachner.These new works, which were composed in a liturgical style, fit in with their much older cousins surprisingly well. The Kennerley work, which Angel had commissioned, was a bit too dreary. But the Wachner piece often made a joyful noise and was a lot more fun to be around.The ensemble players were at their best with the Purcell pieces. Their original instruments frequently can be difficult to manage and reluctant to work and play well with others. But, led by artistic director and violinist Kristin Van Cleve, the group maintained an unusually smooth and unified sound on nearly all the works on the program.They especially had some fun with a section The Fairy Queen that saw trumpeter Adam Gordon slip into a room adjoining the stage, where he echoed the efforts of the five players remaining on stage.The most engaging piece of the evening may have been the cheerful and catchy Regina Coeli, a piece by Leopold I, who ruled the Holy Roman Empire from 1658 to 1705 while writing a little music on the side.The work, which also featured Angel, was sweetly simple, while also sounding more sophisticated than might be expected from a monarch slumming it in the concert hall.