Notorious real estate magnate and demolition baron Alonzo Hawk (Keenan Wynn) is ready to build his newest indoor shopping center, the 130-story Hawk Plaza in San Francisco. His only obstacle is the 1892 firehouse inhabited by "Grandma" Steinmetz (Helen Hayes), widow of its former owner, Fire Captain Steinmetz, and aunt of mechanic Tennessee Steinmetz; her displaced neighbor, flight attendant Nicole Harris (Stefanie Powers); and their sentient machines: a 1963 Volkswagen Beetle known as Herbie, "the Love Bug;" an early 20th-century orchestrion that plays on its own; and a retired cable car from the defunct Clay Street Line, known as "Old No. 22."