The play's conceit is described as follows on Wikipedia: "Elwood P. Dowd is an affable man who claims to have an unseen (and presumably imaginary) friend Harvey—whom Elwood describes as a six-foot, three-and-one-half-inch tall pooka resembling an anthropomorphic rabbit. Elwood introduces Harvey to everyone he meets. His social-climbing sister, Veta, increasingly finds his eccentric behavior embarrassing. She decides to have him committed to a sanitarium. When they arrive at the sanitarium, a comedy of errors ensues. The young Dr. Sanderson mistakenly commits Veta instead of Elwood, but when the truth comes out, the search is on for Elwood and his invisible companion."