In the opening credits of Blow-Up, Italian director Michelangelo Antonioni acknowledges that his film is based on "Las babas del diablo" ("The Devil's Drool"), a short story by Argentinean writer Julio Cortázar.

Blow-Up is Antonioni's view of the world of mod fashion, and an engaging, provocative murder mystery that examines the nature of reality through photography. In the sixties, swinging London was seen all over Europe as the center of change and the origin of new trends in music and fashion.

The central character, Thomas, is a high-fashion photographer who lives in mid-1960's London. He has becomes bored with his lucrative career of glamour photography. So he resorts to photographing, in documentary style, the seamy and sordid side of life in London's flophouses and slums.

Casually, he takes candid photos in a deserted park of a lover's tryst-rendezvous between a woman and a middle-aged, gray-haired man. When the woman sees that she is been photographed, she pursues him to ask for the illicit photos, and he imagines that he has witnessed a scene of sexual intrigue - never thinking that he may have accidentally obtained visual, criminal evidence of a murder.

Thomas begins to develop the shots. When he makes enlargements of some of the prints, he discovers what looks like a body. Thomas returns to the park and sees (or imagines he sees) a body. Returning to his studio, Thomas finds out that the blow-ups have been stolen and that the only one left is a very confusing print. Finally, Thomas goes back to the park, but he is not able to find the body.

In the short story by Cortázar, the focus is the seduction scene, whether real or imagined, between a woman, a young boy and a man, just as the murder mystery is the focus of the Antonioni film. Reality becomes a subjective statement in both the story and the film that explores the confusion of events directly or indirectly through the medium of photography.