In the late 1980s, a group of dissident officials in the Soviet Union have grown afraid of losing power as relations improve with the United States. Hoping to oust the Soviet President, they steal a nuclear missile and launch it at Ukraine from a site in NATO member Turkey. Soviet automated defense systems, believing a NATO attack is in progress, execute a measured launch of intercontinental ballistic missiles (ICBMs) at the United States.
The US Strategic Air Command (SAC) scramble its forces. SAC Commander General Renning urges the President of the United States to authorize a full counterattack.
The Soviet President contacts his US counterpart, explaining the dissidents' actions. He asks the US to stand down, but is willing to accept a US counterstrike if it is exactly equal to the Soviet's first strike, costing each side 6 to 9 million people. If the US launches an all-out attack, the Soviets will respond in kind, dooming the planet.
The US President and General Renning argue about the message from the Soviet leader until it appears that the Soviets have launched a second attack. The President authorizes a multi-part all-out attack, with US ICBMs launched immediately, then submarine-launched ballistic missiles (SLBMs) in a few hours, coincident with the arrival of US nuclear bombers over the Soviet Union. General Renning issues the orders just before the first wave hits SAC headquarters, then quickly passes command of SAC to "Alice"—code name of the US General in command of Looking Glass, a flying command platform for the US military.
The President is ushered to Marine One. As the helicopter lifts off, he learns that the second Soviet attack was not directed at the US but at China – which had launched their own missiles at the Soviets, adding untold millions of deaths in those two countries. As he tries to cancel his orders for the all-out US retaliation, a nearby nuclear detonation knocks his helicopter out of the sky.
A B-52 bomber, callsign "Polar Bear 1", takes flight just minutes before an ICBM wipes out Fairchild Air Force Base. The bomber is piloted by Major Cassidy and his female co-pilot (and secret lover) Captain Moreau. The crew is shaken by the unfolding events, with crewman Tyler struggling with the fact that his family was just killed at Fairchild.
A US Admiral, code name "Harpoon", is in command of Nightwatch, a flying command platform for the US President. With the President gone, they swear in the Secretary of the Interior as the new President, code name "Condor". Harpoon informs Condor of the last communication from the Soviet President, the mistake regarding China, the matching damage already done by the initial retaliation with US ICBMs, and advises that the US agree to the ceasefire. Colonel Fargo, a hawkish advisor on Nightwatch, believes the Soviets are playing a trick, advising Condor that the only path to victory is quick destruction of the Soviet Union.
Polar Bear 1 is attacked by a trio of MIG-25s over Alaska. The crew drop one of their nuclear bombs on the side of a mountain range, using the other side of the mountain to shield their plane from the blast while the MIG-25s are destroyed.
Condor agrees with Col. Fargo's plan to move forward with a SLBM and bomber attack. Harpoon disagrees and attempts to hide his nuclear authentication codes, but they are forcibly taken by Col. Fargo. Fargo and Condor contact Alice, giving the authentication codes and ordering him to execute the remainder of the attack plan. Alice advises against this course of action, but obeys his orders and begins to organize the bombers for the attack.
The attack orders are received by Polar Bear 1. Moreau argues that their target will kill off all Soviet leadership, leaving nobody to "turn [the war] off". Cassidy hands her a suicide pill, but then breaks down and begs her not to go. The crew agree to turn back – though Tyler suddenly becomes despondent over the death of his family and has to be restrained. He later attempts to shoot the pilots for cowardice, then uses an ejection seat, blowing everyone but the two pilots out of the aircraft.
The original President has survived the crash of Marine One, and a family gets him to a FEMA emergency shelter. By way of a FEMA communication system, he learns what Condor is doing, then manages to contact the Soviet President. The Soviets promise to stand off for one hour to see if the US will recall its bombers.
Looking Glass notices that Polar Bear 1 has abandoned its attack run, and sees that the Soviets have turned one of their own bomber squadrons back in response. Alice begs Condor to view this as a sign that the Soviets are willing to call a ceasefire and asks for permission to recall all US bombers. Condor instead orders Alice to send US carrier-based fighters to shoot down Polar Bear 1 as traitors. When Alice hesitates, Fargo informs Condor that they can figure a way to send the launch commands from Nightwatch, at which point Condor dismisses Alice and cuts off communication with Looking Glass.
The real President contacts Looking Glass. He lost his authentication codes in the helicopter crash but calls Alice by his real name as proof of who he is. Alice and his Looking Glass staff agree to follow the real President's orders and order a recall of the bombers.
Two American carrier-based fighter jets intercept the crippled Polar Bear 1, now flying low over the Pacific Ocean. As the fighters begin their attack run, they receive word that their ship has been hit by a Soviet torpedo and is sinking. Doomed to run out of fuel in the open ocean, they bid Polar Bear 1 good luck.
The real President finally connects with Condor. Condor doubts it is him, which Col. Fargo reinforces by implying that the Russians have impersonators. Condor states that the President he knew would want a military victory, and disconnects. Fearing the President "impersonator" might try to cancel the US SLBM launch, Condor orders the Nightwatch staff to find a way to connect to the US submarines.
The Looking Glass staff and crew agree with Alice's remaining option – ram Looking Glass into Nightwatch before Condor can send his launch orders. Looking Glass had been flying to rendezvous with Nightwatch for some time, and now makes all effort to close the remaining gap. Fargo realizes what Looking Glass is doing, so Condor orders his pilot to fly evasively until the launch orders can be transmitted. Realizing what Condor and Fargo plan to do, the Nightwatch flight crew sacrifice themselves, turning Nightwatch into the path of the oncoming Looking Glass. Once the two planes are destroyed, the real President successfully issues a message to stand down the US attack.
Principal photography took place from August 7 to late September 1989. The use of military hardware such as the B-52 bomber and Boeing E-4 enabled a realistic account of the Strategic Air Command in action.
There are two major differences between the plot of the novel and the film, the first being that the crisis in the novel is started by a deliberate Soviet attack to counter the US military buildup with which they are unable to compete. The other major difference in the film is the romantic subplot between Moreau and Cassidy, which is absent from the book; the characters there actually mocking the idea of such a relationship between them.
Contemporary reviews of By Dawn's Early Light centered on the confrontation by nuclear powers and gave it accolades. "There never has been a made-for-cable movie as sleek and efficient as By Dawn's Early Light. Fast-moving, complex, and only occasionally a bit hokey, it's by far the best original movie project HBO has overseen." "Boasting high production values, okay special effects, and a surprisingly top-notch cast... a thrilling drama that is your better-than-average made-for-TV movie." More recent reviews were similar: "Probably the end of the line for Cold War confrontation on this scale, but compelling drama nonetheless."
In 1990, James Earl Jones was nominated for an Emmy for Outstanding Supporting Actor in a Miniseries or a Special and Matte World Digital won for Outstanding Achievement in Special Visual Effects.