Danny Kaye plays a double role as a pair of estranged "super-identical twins". Despite their almost indistinguishable looks, the two have very different personalities. Buster Dingle, who goes by the stage name "Buzzy Bellew", is a loud and goofy performer at the Pelican Club, while Edwin Dingle is a studious, quiet bookworm writing a history book. The two brothers have not seen each other for years.
Buster becomes the witness to a murder committed by mob boss "Ten Grand" Jackson and is promptly murdered himself. He comes back as a ghost, calling on his long-lost brother for help to bring the killer to justice. As a result, the shy Edwin must take his brother's place until after his testimony is given.
In the meantime, he has to dodge Jackson's hitmen and fill in for Buster at the nightclub. To help him out, Buster – who cannot be seen or heard by anyone but Edwin – possesses him, with outrageously goofy results.
Edwin, possessed by Buzzy, performs a bit where he pretends to be a famous Russian singer allergic to flowers. A vase of flowers is nonetheless placed on a table near him, and his song, "Otchi Chornya", is frequently interrupted by his loud and goofy-sounding sneezes.
The love interests of the brothers further complicate the situation; while the murdered Buster was engaged to entertainer Midge Mallon, librarian Ellen Shanley admires Edwin.
In the end, Ellen marries Edwin, while Midge consoles herself by marrying the owner of the Pelican Club.
