Seymour (Rick Moranis) is the clumsy employee of Mushnik's Flower Shop on skid row, where he daydreams of Audrey (Ellen Greene), his coworker. After no business, Mr. Mushnik (Vincent Gardenia) decides to close the shop. Seymour and Audrey tell him that they think displaying something interesting, strange, and new in the window will attract business. Seymour brings up the perfect plant for the job: a flytrap-esque plant he calls Audrey II (voiced by Levi Stubbs, of the Four Tops). The plant immediately attracts business. After the store closes, the plant begins to wilt, and Mr. Mushnik orders Seymour to fix it.
That night, Seymour discovers what Audrey II eats: blood. Seymour feeds the plant his blood, and as a result, it gets bigger and bigger. When Seymour becomes unable to keep feeding it, the plant begins to talk and urges him to kill people and feed them to him. Audrey II promises him rewards, and that he'll bring him business, luxuries, everything he's ever wanted, and Audrey.