The story of Tondal's Vision dates back at least to the 12th century, when it was written down in Latin by an Irish monk; in subsequent centuries it was transmitted over much of Catholic Europe in several languages. (Livljanic uses a version in medieval Croatian from a manuscript compiled for a convent on the Dalmatian coast.) The plot prefigures that of Dante's Divine Comedy (and, for that matter, Dickens's A Christmas Carol): A knight named Tondal has a dream in which an angel leads him on a journey in which he sees both the damned souls in hell and the blessed in paradise.

Tondal's Vision is a prose tale, not a liturgical drama like the 13th-century Play of Daniel and Play of Herod, or an allegorical morality play like Hildegard von Bingen's Ordo Virtutum. What Ensemble Dialogos performs is, for all its medieval materials (and mysticism), a piece of contemporary music-theater.

For her performing version, Livljanic has set the text of the story (as preserved in the Croatian manuscript) to music using chant melodies and formulas (as transmitted in manuscripts and orally) from the Croatian coast. Inserted into the narrative at key points are pieces of liturgical music from medieval Dalmatia — often pieces referred to directly in the story's text — some in Latin, some in the old Croatian dialect of Church Slavonic.

The result offers a striking variety of idioms: single-voice plainchant in a rhythmically free style that any fan of Hildegard's music will recognize; part-singing with crunching dissonances and surprising chromatic turns that come from a Balkan tradition unfamiliar to Western ears; smoothly flowing melodies with sweet parallel thirds not unlike what one might hear in a Russian Orthodox church today.

Sandra Hrzic has provided a simple staging with slow-moving stylized gestures and costumes that seem to allude to (rather than mimicking) nuns' habits. The effect puts a viewer in mind of a small group of nuns enacting a ritual together, though the performance never presents itself as a historical reconstruction or reenactment.

Dialogos gives four performances of Tondal's Vision on this North American tour:

• New York City - Sunday, February 18 - Corpus Christi Church (Music Before 1800, www.mb1800.org)
• Wellesley, MA - Tuesday, February 20 - Houghton Chapel (Wellesley College, www.wellesley.edu)
• Vancouver, BC - Thursday, February 22 - University of British Columbia Recital Hall (Early Music Vancouver, www.earlymusic.bc.ca)
• Kansas City - Saturday, February 24 - Grace and Holy Trinity Cathedral (Friends of Chamber Music, www.chambermusic.org)

For more information about Dialogos, visit www.ensemble-dialogos.org.