This is a three act play retelling an Arthurian legend (particularly the Lancelot and Guinevere thing). Published in 1927, this piece is now 80 years old, but it reads older than that. Set in the 10th century in England, the characters all speak Middle Englishesque, which is not historically accurate (Middle English started in the next century, and it certainly wasn’t spoken in 1927 on the east coast of America). As it’s not a direct retelling of the legend of Lancelot, the suspense kept me moving even through the stilted prose.
I read most of my Millay in early college, and my structured poetry of the time reflects her influence. Casting love poetry and whatnot into Middle English turns of phrase and relying upon iconic imagery of the period. I later moved a bit beyond it, but I still appreciate it enough that I enjoy Millay more than McKuen.