Dominick Argento’s The Voyage of Edgar Allan Poe was the signal hit of Lyric Opera’s season. Now his 1971 opera Postcard From Morocco, in a staging also by Frank Galati, promises to do the same for Chicago Opera Theater. A long one-act, Postcard has a plot that’s as old (and contrived) as Grand Hotel. On the eve of World War I, seven travelers find themselves stranded in a hothouse train station somewhere in Morocco. As the action unfolds, each character clings obsessively to a box or suitcase, as if hiding from view relics of a painful or cherished past. The opera then proceeds like group therapy–exorcising these psychological demons through cruel confrontations and comforting coincidences. Argento and his librettist John Donahue have deftly paced the episodes of revelation so that when the denouement comes–when the protagonist’s box is forced open–it is at once startling and moving. The eclectic, mood-evoking score–with echoes of Britten, Stravinsky, and Puccini–is vintage Argento, flowing gracefully and poetically. In this production the fine young cast (assembled by COT founder Alan Stone) is headed by Phyllis Pancella (as Lady With a Hat Box), Gloria Capone (as Lady With a Cake Box), and Matthew Lord (Man With Paint Box). In charge of one of the best midsize pit orchestras is Hal France, a seasoned interpreter of contemporary American operas. Wednesday, 7:30 PM, next Saturday, May 11, 8 PM, and next Sunday, May 12, 3 PM, Athenaeum Theatre, 2936 N. Southport; 663-0048.