Elwood P. Dowd insists on including his imaginary friend Harvey, a six-and-a-half-foot-tall rabbit, in all of his sister Veta’s social gatherings. To avoid future embarrassment, she has Elwood committed to a sanitarium. Problems arise when Veta is mistakenly assumed to be on the fringe of lunacy when describing her own visions of Harvey. The doctors commit Veta instead of Elwood, but when the truth comes out, the search is on for Elwood and his invisible companion who have a surprising influence on all who encounter them.
