Seymour works in a skid row florist shop and is in love with his beautiful co-worker, Audrey. He creates a new plant that not only talks but cannot survive without human flesh and blood.

Nerdy Walter Paisley, a maladroit busboy at a beatnik café who doesn't fit in with the cool scene around him, attempts to woo his beautiful co-worker, Carla, by making a bust of her. When his klutziness results in the death of his landlady's cat, he panics and hides its body under a layer of plaster. But when Carla and her friends enthuse over the resulting artwork, Walter decides to create some bigger and more elaborate pieces using the same artistic process.

In the Windy City, the mob infiltrates a powerful union.