For the five hours of this legendary tragedy, all the singers involved will be put through their paces. (When Wagner wrote the opera, others thought it couldn't actually be staged because of its length and the difficulty of the roles. And legend has it that it killed the first tenor who sang the Tristan role.) HGO has also brought in as its leads two singers known for their mastery of this repertoire: Canadian tenor Ben Heppner and Swedish soprano Nina Stemme, who will be making their HGO debuts. ''Wagner's operas, really, a lot of what they are about is showing how people interact on the surface while at the same time, this music that happens underneath, particularly the orchestra, shows the real feelings and emotions and thoughts and troubles and joys,'' McKinny says. And in some sense, he says, it's fascinating to him that such a ''broken man'' as Wagner was able to write such sublime music. ''There's something appealing to me that a man who obviously had so many issues as a person can write this music that quite often gets down to the kernel of truth about what human beings are.''
6:30 p.m. April 18, 24, 27 and May 2; 2 p.m. April 21 and May 5. Wortham Theater Center, 500 Texas. For information, call 713-228-6737 or visit houstongrandopera.org. $15 to $386.
Thu., April 18, 6:30 p.m.; Sun., April 21, 2 p.m.; Wed., April 24, 6:30 p.m.; Sat., April 27, 6:30 p.m.; Thu., May 2, 6:30 p.m.; Sun., May 5, 2 p.m., 2013