It was probably sheer luck that caused the many radio telescopes of the Argus project to point at the star system of Vega at exactly the right time. If the telescopes hadn't been looking at the star that night, the scientists watching over the signals picked up by the telescopes may never have discovered the first sign of life outside our planet. But they caught a broadcast of prime numbers, a message that would change the course of Earth's history forever. That is the premise of Carl Sagan's novel Contact. Based on Sagan's own studies as an astrophysicist and philosopher, Contact provides a possible glimpse of the world's reaction to extraterrestrial life.
The heroine of the story is Eleanor Arroway, an astrophysicist and radio telescope engineer, working on the Search for Extraterrestrial Intelligence (also known as SETI). The book opens with a description of her childhood. The young Ellie Arroway is curious and skeptical, asking questions about everything. As she grows from a young girl to a mature woman, she gains a rebellious streak, asking tough questions about religious contradictions and refusing to listen to her stepfather under the pretense that he is not Ellie's true father, who passed away before Ellie reached adolescence.
After her college and graduate school years, she works as an astronomer with radio telescopes. She originally works on more 'conventional' studies, but as the years pass, she decides to follow her interests and work on the SETI project. She is assigned to work on the Argus project, a large radio telescope array designed to search the farthest reaches of the universe. One night, the radio telescopes pick up a signal: prime numbers, which would be extremely unlikely to be created by natural phenomena. After meticulously checking for hoaxes and radio interference, the Argus scientists confirm that the message is coming from the star system of Vega, twenty-six light years away. It is almost definitely from another civilization.
Prime numbers are not the only thing being transmitted in the Message. Two additional messages are broadcast: one is a playback of the very first Earth transmission into space, replayed to the planet to show that Earth has been noticed. (Unfortunately, the first transmission involves Hitler, to the embarrassment of many.) The second and far more important message is a blueprint for a machine, one designed to take five people somewhere. Nobody knows where, or if the machine will even take anyone anywhere. Speculation of doomsday devices are suggested, and many nations debate over who would build the Machine, which nations would have representatives in the Machine, or if the Machine will even be built at all.
Beyond the scientists and politicians, the religious forces weigh in on the subject. Some argue that the Message is from God, others suggest Satan. Two prominent American preachers, Rev. Billy Jo Rankin and Palmer Joss meet with Eleanor Arroway to discuss the religious implications of the message. Both preachers are distrustful of the scientists working on the project and argue that religious leaders should be on hand to help translate the message. As more and more of the Machine blueprints are recorded, the more and more the tensions between the religious and the scientific increase.
Eventually the Machine is built, but destroyed by a bomb placed on one of the parts. The American who was supposed to go in the Machine, David Drumlin, is killed in the explosion. This causes the American representative to Vega to be Eleanor. A second machine is built near Hokkaido, Japan, and Ellie and four other people representing different nations, cultures, and religions board. The Machine is activated, and the five of them are shot into a wormhole. They are shot in a kind of cosmic mass transit system, viewing all sorts of star systems (one of which is Vega) and end near the center of the galaxy, where a large docking station awaits.
The five envoys to the galaxy find themselves on what appears to be an Earth beach. While the others explore, Ellie stays behind on the beach. Waiting for a welcome from the extraterrestrials, she instead receives a welcome from someone in her childhood: her father, Theodore. Only it is not her father, but one of the intelligent beings who is hoping to make Ellie at ease. Ellie asks as many questions of the alien as she can, and discovers that there is a long-lost species who has created the tunnels she and her companions traveled through, as well as the strong possibility of a Creator of the universe. Ellie's father suggests that she look at the number pi for a signature.
When the five ambassadors to space return, they are told that they went nowhere and were only out of contact for about twenty seconds. They claim that they have been gone for about eighteen hours, but they have no evidence, as Ellie's camera has recorded only silence. Ellie is accused first of delusions, but later of helping to perpetrate a hoax. She is unable to prove her story, and thus many people are unconvinced. However, there are still many who believe her, including Palmer Joss. There is one bit of evidence to back Eleanor's story up: her camera may have only recorded static, but it recorded eighteen hours of static, not twenty seconds.
The story ends with Ellie taking her dad's advice, and scanning pi for a signature. She finds it, in base-eleven: a circle made of ones and zeroes. A new Message is discovered.