February 23, 2016

One minute, Dotty’s eyes are clear, and her mind is as steely sharp as her tongue. A minute later, clouds seem to shroud those big, bright peepers, and she has the bewildered look of a toddler who’s lost track of her mother at the mall. Dotty (Marjorie Johnson), the widowed matriarch of a black middle-class family from Philadelphia, is 65, and although she mostly avoids directly admitting it to anyone — sometimes even to herself — she has Alzheimer’s. In Colman Domingo’s thoroughly entertaining comedy-drama “Dot,” Dotty’s failing mind becomes the focus of a fraught family gathering. The play, which opened on Tuesday at the Vineyard Theater, is an impressive advance for Mr. Domingo, also a gifted musical-theater performer, whose previous plays include the autobiographical “A Boy and His Soul” and “Wild With Happy.”