It takes an artist of the stature and extraordinary talent of Wiest to keep Caswell's fragmented play from flying off in all directions as it veers from reality to fantasy and from flashback to the present. Or, is the entire plot, which takes an embittered 75-year-old widow from the depths of the Mid-west to the depths of Hollywood, just a figment of her yearning imagination? The tale of Meryl Kowalski (both name…