"Seren" means star in Welsh, and few are the stars that burn more intensely than trebles, or boy sopranos, as Americans have it, for they have only a very short time, sometimes measured in months before it's all over. Treble Cai Thomas seemingly emphasizes this by inviting Aksel Rykkvin as a guest on Karl Jenkins' Ave verum. Just a few years ago, it was Rykkvin who was the star treble, but now he's a baritone. Thomas sets out here to play to his strengths. He has a Welsh song to reflect his heritage, the ubiquitous "Pie Jesu" of Fauré, a couple of slow Handel tunes, some modern crossover material, and a few pieces of pop minimalism. Perhaps Thomas' strongest pieces are the ones that stand out from the program: Charles Villiers Stanford's The Blue Bird and a really haunting version of the folk song The Ash Grove, but all of the music inhabits a moderate vocal range, is in moderate tempos, varying only in flavor. Thomas's voice rests easily in all the pieces, and, unstressed, it's gorgeous, with startling clarity and a tinge of melancholy that's especially affecting. Perhaps to add more variety, Thomas uses several backing groups; this works well, with his voice foregrounded slightly differently each time. Savor the voice while you may.