Which holiday is the setting for the episode 'The Masks'?

The setting of “The Masks” is Mardi Gras.

The episode takes place on Mardi Gras night, when Jason Foster gathers his unpleasant relatives for a final family celebration. Foster is elderly and dying, while his daughter Emily, son-in-law Wilfred, grandson Wilfred Jr., and granddaughter Paula are chiefly interested in inheriting his fortune. He uses the holiday’s masking tradition to expose what he sees as their true personalities.

Each relative receives a grotesque mask that represents an inner flaw: cowardice, greed, brutality, or vanity. Foster wears a skull mask, presenting death as the opposite of his own lively spirit. He adds a condition to his will: the family must keep the masks on until midnight or receive only their train fare home.

“The Masks” first aired on March 20, 1964, during the fifth and final season of the original series. Rod Serling wrote it, and Ida Lupino directed it—the only episode of the original Twilight Zone directed by a woman. Mardi Gras is therefore more than a backdrop: its disguise-and-revelation tradition drives the plot and its supernatural punishment.