Chris Cronyn (Peter Graves) and his wife,Linda Cronyn (Andrea King) meet Dr Mitchell (Lewis Martin) at an observatory in Southern California. He explains the experiment that has been ongoing to send and receive messages to Mars. Dr Mitchell shows the couple a number of photos that have been taken that seem to show the Martians have melted their planetary icecaps and are irrigating the desert regions of the planet.
Encouraged by the information from Mitchell, Cronyn plans to send another signal. His wife expresses doubt about contacting the Martians; shes worried what might happen. Slowly Cronyn argues her around and she agrees to continue with the research. At a Russian research station in the Andes Mountains, agents break in and question Franz Calder (Herbert Berghofare) who is also trying to contact Mars.
Calder refuses to be intimidated by the agents and tells them he has discovered the Americans have made contact with the Martians, and that hes been able to intercept the messages. Back at the Cronyn's, Admiral Bill Carey (Walter Sande) pays a surprise visit after hearing about the project. Cronyn admits the biggest problem is the Martians are only replying with the same message that Cronyn is sending.
Overhearing the conversation Cronyns son suggests possibly sending a mathematical equation and see if they recognize what it is. The suggestion makes sense and a message is quickly composed and sent.As they wait for the return signal. Cronyn explains the role Dr Calder played in developing the technology in use, he tempers knowledge of the mans brilliance with the knowledge he is a wanted Nazi war criminal.
Right on time, Cronyns instruments light up, a message is being received. The Martians have completed the equation. News spreads quickly about the break through. As weeks pass, more and more information is exchanged with Mars, information such as Mars having unlimited power, excess of food and a life span of over three hundred years.
The news brings economic collapse around the world, first agriculture then the mining industry collapse, eventually even the banking industry is affected. The stress of the discoveries begins to tell on the Cronyn family. The military take control of the situation by forcing all signals from Mars to be sent directly to the Pentagon, where the messages will only be released once there is evidence the message wont have an adverse effect.
In Moscow, the Russians have become encouraged by the economic collapse begin to consider going to war. The leaders of the US come to the same conclusion. War will be inevitable with the Soviet Union. The American President decides that a group the remaining group of 13 messages will remain uudecoded. The President also tells Cronyn the Russians have found a way to decode the messages because they released the text of one of the messages before the US did.
A new message is received, and translated. Although a little ambiguous It seems to indicate that the Martians made contact with Earth some 2000 years ago, possibly in the form of Jesus Christ. The next message has even stronger religious message. All over the free world churches of all faiths are filled to bursting point. In the Soviet Union a group of peasants dig up hidden relics religious relics, hidden since the time of the revolution.
The villages gather around and begin to celebrate an outdoor mass. Suddenly a truckload of armed police arrive and machine gun the whole congregation. Yet another message is decoded. This time Calder transmits the text to the Soviets. The message specifically points evils of tyrants and the true way is through God. Shortly after delivering this message Calder dies in an avalanche.
Reports begin coming in to the central committee from all over Russia of villages rising up to fight the local Soviet officials. The Soviets decide that population redistribution may be required. At the Kremlin the phones stop working, then the power is cut. Singing can be heard from the street. The Soviet Premier realizes it is a religious hymn. Gunfire begins to echo through the streets and a nearby building explodes into flames.
Suddenly a TV broadcast is seen around the world sent from Moscow. It is the British Ambassador reporting that the communists have been over thrown, and the Patriarch of the Russian Orthodox Church has taken power. His first announcement is to withdraw all Soviet troops from around the world. Sometime later Calder breaks into the Cronyns home, he goes on to explain he survived the avalanche and the long trip he undertook to get to the US.
Calder reveals that the messages were not real and no one has successfully contacted Mars. He proves that he invented the messages, simply to amuse himself Mrs. Cronyn realizes that Calder sent some of the messages, but he was not responsible the religious messages. Calder brushes her argument aside and is going to reveal the truth to the world that he faked all of the messages.
His proof will be the fact the Martians have not replied since the avalanche destroyed his installation. The Cronyn's realize the only way to stop Calder is to blow up their installation. Mrs. Cronyn releases a valve that floods the room with hydrogen. As she goes to light a cigarettes, the receiver begins picking up a message from Mars.
Calder realizing he is caught in his own lie panics, fires his gun, blowing up the building and killing the occupants. Sometime later The President is delivering a eulogy for the Cronyns. He reads the first few words of the last message before the explosion interrupted the transmission, "Ye have done well my............"