I'm sorry, Emerald, if I am rude
But in this queer dark unexpected place
My words as well drop unexpectedly
I feel I'm in a dream.— Lila in A Christmas Play, Tales Before Tolkien, p. 402
Not intended for publication or professional staging, Lindsay's Christmas Play was a seasonal diversion for the family, and was probably written in the 1930s. It remained something of a rumour till Douglas A Anderson unearthed it for publication in his anthology of short fiction by writers that may have inspired J R R Tolkien, Tales Before Tolkien.
The fairy Emerald wants to find princes as husbands for the three daughters of a woodcutter, but Titania, Queen of the Fairies, says only two princes are to be found, and leaves the choice of the third husband to Mother Nightshade, a witch of evil repute.
More detailed plot summary here.
A Christmas Play
You can read an interview with Douglas A Anderson about Tales Before Tolkien here.