NEW YORK — The Troubles of Tristan, Chapter V: Ben is Back, but Deborah is Down.

It’s been more soap opera than grand opera at the Metropolitan Opera these days where Wagner’s “Tristan und Isolde” is concerned.

Since the revival opened its six-performance run on March 10, every performance has been marked by one casting crisis or another, and no single pair of singers has made it through the entire opera more than once.

Tuesday night was notable for the return of tenor Ben Heppner, who was to have sung Tristan in all six performances but missed the first four because of a bacterial infection.

Heppner, one of the few singers today with the size of voice, beauty of tone and stamina to do justice to the punishing role at a big house such as the Met, was in splendid voice for much of the evening. His one vocal weakness is a tendency to crack on high notes, and he did that a few times in his fevered outcries near the end, but that scarcely marred the intensity of his performance.

Heppner’s recovery is welcome news for Wagner fans, as he prepares for his first staged performance in another taxing part, the title role in “Siegfried,” which he is scheduled to sing in Aix-en-Provence, France, in June and July.

Isolde was to have been soprano Deborah Voigt, but she was knocked out by the same stomach ailment that caused her to rush offstage in the middle of Act 2 during the second performance on March 14.

Her replacement, Janice Baird, had made her Met debut in that earlier performance and won warm applause for her courage and professionalism. This time she drew cheers for her singing as well. Given a chance to warm up and sing an entire performance, she made a striking impression. The recurring tendency to sing flat that marred her debut was much less apparent, especially when she was matching Heppner decibel for decibel. And she threw herself into the emotions of the role as well — the humiliation and rage of Act 1, the passion of Act 2, and the grief after Tristan dies in Act 3.

The rest of the cast has been the same throughout, except for one scheduled change Tuesday. Richard Paul Fink brought his sturdy baritone and sympathetic presence to the role of Kurwenal, Tristan’s trusted friend.

With one final show Friday, there’s still a chance the team of Voigt and Heppner will get to perform the opera together.