Florist shop owner Gravis Mushnick has two employees, Audrey Fulquard and Seymour Krelboined. Located on skid row, Mushnick's rundown shop gets little business. When Seymour fouls up a floral arrangement for dentist Dr. Farb, Mushnick fires him. Hoping to change his mind, Seymour talks about a plant he has grown from seeds he got from a "Japanese gardener over on Central Avenue."[20] Seymour named the plant "Audrey Jr.", which delights Audrey.

However, when finally shown the plant, Mushnick is unimpressed. Seymour suggests that Audrey Jr.'s uniqueness might attract people to see it, and Mushnick gives him one week to revive the plant. The usual plant food does not nourish it, but when Seymour accidentally pricks his finger, he discovers that the plant craves blood. Fed on Seymour's blood, Audrey Jr. begins to grow. The shop's revenues increase when customers are lured in to see the plant. Mushnick tells Seymour to refer to him as "Dad" and calls Seymour his son in front of a customer.

The plant develops the ability to speak and demands that Seymour feed it. Now anemic, Seymour walks along the railroad track. Throwing a rock to vent his frustration, he inadvertently knocks out a drunken man who falls on the track and is run over by a train. He tries to get rid of the body by burying it in a yard but is nearly caught each time. Guilt-ridden, Seymour decides to feed the mutilated body parts to Audrey Jr. Meanwhile, Mushnick returns to the shop to get cash and secretly observes Seymour feeding the plant. Mushnick considers telling the police but hesitates after seeing the line of customers at his shop the next day.