The speaker wakes before dawn on a sleeping porch and finds a firefly on the screen beside the bed, still flashing long after the other fireflies have gone to rest. It seems a little foolish, a lone light repeating its signal into the damp morning. The speaker picks it up and, carrying it to the door, imagines herself as the old woman in a fairy tale who catches a magical creature and refuses to release it until it grants her wishes: gold, a castle, endless happiness.
Then the poem turns. She doesn't bargain at all. She simply lets the insect go, and it flies off "pleading" over the wet grass. The mood is quiet, tender, and a little wistful. The speaker recognizes how easily we want to demand something grand from a small, fragile thing, and chooses mercy instead. The firefly's lonely flashing may also echo her own wakeful, solitary hour.