I think the summary of the ballet
rg posted in #20, above, is skimpy, although it gives some indication of what happens on stage. To round it out, here's the rest of Denby's remarks, the passage just before the part I quoted before, which takes more account of what may happen in us onlookers:
To Poe lovers in the dance public... the mysteriousness of Balanchine's Night Shadow [the original title]... is recommended. Mysterious is the interaction of its elements: the vapid ballroom dances; the winsome exhibition numbers that have a perverse and cruel undertone; the elaborate, encircling artifices of the coquette's pas de deux; the directness and space of the sleepwalking scene; the massed mime chorus in unison at the end.
How effective the MCB performances will be remains to be seen; Denby was writing about the premier ones, supervised by Mr. B., and Arlene Croce wrote in
Playbill, Jan.-Feb. 1970, about some more he presented (quoted in Nancy Reynolds's
Repertory in Review):
The emotions of the ballet comes in a series of nervous shocks, as deeply pleasurable as in a horror story. The ending - is there a finer one in all romantic ballet? - is high traumatic bliss. The pas de deux roles are unthinkably reversed. Now it is the Sleepwalker who claims the inert body of the Poet, accepts it in her arms, and carries it away forever.
The ideas in La Sonnambula are perfectly clear derivations from the romantic ballet of the nineteenth century, but they are forced even beyond the neurotic extremism of Giselle and La Sylphide. The Poet's character as a hero who engages a divine force is not morally shaded. When he dies he is vindicated, but in a manner that anathematizes not only the explicitly anti-romantic society on the stage but all humanity as well. The ironclad arrogance of the gesture makes the real suffering we've witnessed seem like a personal secret accidentally disclosed. It keeps you at a distance, though you may find yourself in tears.
Reynolds also quotes Maria Tallchief, the original Coquette:
Balanchine's so mystical, which not many people realize. Look at Night Shadow, where [at the end] all you see is people looking up, at something - a light. People so often think of him as someone who does steps - mechanical, dry steps - and this is so completely opposite from what he is. To me, his great glory is his wonderful mysticism - he's a poet, really, more than anything else.