So, a guy walks into a bar ...

It's the first line of a thousand jokes, but it's also the unlikely beginning to the rock opera the Trans-Siberian Orchestra performed at Mellon Arena Sunday.

At the second of two shows the group played, the TSO opened with an 85-minute song cycle formed by pieces from its trilogy of Christmas-themed discs. Narrator Bryan Hicks, speaking in deeply-intoned rhyming couplets, acted as the bar-bound protagonist. There his character met an old man who spun a yarn about an angel sent to Earth to investigate man's true worth.

With that setup, the TSO proceeded to bridge together songs steeped in Broadway musical storytelling, classical instrumental precision and heavy metal bombast. Instrumentals combining Christmas carols ("O Holy Night" with "O Come All Ye Faithful" and "Joy to the World" with "Good King Wenceslas") segued into a wide range of narrative pieces.

The songs sung by Jay Pierce were best-received. "Prince of Peace" featured just Pierce's vocals and musical director Bob Kinkel's keyboards, allowing Pierce plenty of room to powerfully and soulfully sing of Christ's birth. "Good King Joy" turned into more of a gospel rave-up through the force of Pierce's vocal personality.

Pittsburgher James Lewis brought Joe Cocker-esque grit to the two tunes he sang from the perspective of a lonely man praying for his daughter's return home. He brought just the right amount of ache to "Ornament" and plenty of celebratory gusto to "This Christmas Day."

Eventually, the story linking the songs ended when the angel returned to heaven, reporting that the best of us is in our wishes, prayers, tears and songs. The old man who told the story mysteriously disappeared, leaving no footprints in the snow. Our narrator then went home and, for the first time since childhood, "dreamed a Christmas dream." It's not much of a punch line, but it concluded a set of good cheer and seasonal reminders to work for peace.

For those who've made the TSO's holiday spectacular a tradition, the show was essentially the same rock opera played here the past two Decembers by the same set of musicians.

The second set of the show was again a hodgepodge of leftover songs from the Christmas albums, classically themed pieces and a random rock radio staple ("Layla" replacing last year's "Rock and Roll" at this show). There was also a keyboard duel between Kinkel and Mee Eun Kim. While still delivered to the accompaniment of flames and lasers and executed with aplomb, the second-set songs lacked the Christmas suite's emotion and sense of purpose.

Clearly this formula is one the TSO has taken to the bank, though, as this is one of two versions of the TSO touring simultaneously. In the spirit of holiday giving, the group donated $1 of the price of every ticket to Columbia Gas' Dollar Energy Fund, presenting a $23,365 check at the start of the show.

No joke -- the Trans-Siberian Orchestra delivered a traditional Christmas message in a singular and eye-poppingly nontraditional format.