In 2005, Afghanistan, Taliban leader Ahmad Shah is responsible for killing over twenty United States Marines, as well as villagers and refugees who were aiding American forces. In response to these killings, a United States Navy SEALs unit is ordered to execute a counter-insurgent mission to capture Shah. As part of the mission, a four-man SEAL reconnaissance and surveillance team is tasked with locating Shah. The four SEALs include team leader Michael Murphy; Marksmen Marcus Luttrell and Matthew Axelson and communications specialist Danny Dietz.
The team is inserted into the Hindu Kush region of Afghanistan, where they make a trek through the mountains where they begin to encounter communications problems. Arriving at their designated location, the SEALs are accidentally discovered by local goat herders, whom the SEALs detain. Knowing that if they release them, the herders will likely alert the Taliban to their presence, the team is split about whether to kill the herders or not. After a brief debate, the team chooses to release them and abort the mission, but before they can escape, they are attacked by Taliban forces. Although the SEALs kill several Taliban gunmen, they are heavily outnumbered and at a disadvantage, and the men take on various wounds during the firefight, worsened when they jump off the edge of a ridge and into a large ravine.
Despite their injuries, the SEALs make a defensive retreat through the steep woods. Dietz begins to lose consciousness and shouts questions to Luttrell, unwittingly revealing the team’s position. Murphy and Axelson jump off another ridge to lead the escape while Luttrell tries to carry Dietz down the mountain, but Dietz is shot again; the impact forces Luttrell to lose his grip and fall off the cliff. A dying Dietz remains at the top of the cliff and is killed. Murphy attempts to climb back up the cliff to get a phone signal in order to call for support via satellite phone with Axelson and Luttrell providing cover fire. When he finally reaches higher ground, Murphy is able to alert his unit of his team’s predicament and request assistance before he is killed.
In response to Murphy’s distress call, a quick reaction force made up of fellow SEALs boards Chinook helicopters and heads toward the location without gunship escort. When they arrive, the Taliban shoot down one of the helicopters, killing all eight Navy SEALs and eight Special Operations aviators aboard, including Commander Kristensen, while the second helicopter is forced back. Luttrell and Axelson are left to fend for themselves again. Axelson attempts to find cover but is killed when he leaves his hiding spot to attack several approaching insurgents. When Luttrell is discovered by the Taliban, one of the insurgents fires a rocket-propelled grenade, and its impact throws him to the bottom of a rock crevice where he is able to hide from the Taliban and eventually escape.
Luttrell stumbles upon a small body of water where a local Pashtun villager, Mohammad Gulab, discovers him. Gulab takes Luttrell into his care, returning to his village, where he attempts to hide Luttrell in his home. Gulab then sends a mountain man to the nearest American base to alert them to Luttrell’s location. Taliban fighters arrive at the village to take Luttrell, but Gulab and the villagers intervene, threatening to kill the fighters if they harm Luttrell. The fighters leave, but later return to punish the villagers for protecting Luttrell. Gulab and his villagers are initially able to fend off the attackers but are nearly overrun and Luttrell is badly wounded before American forces arrive and defeat the advancing Taliban. After thanking the villagers who had saved him, Luttrell is evacuated. He almost succumbs to his injuries but is revived in time.
Images of the real Luttrell, Gulab and the fallen service members killed during the mission are shown during a four-minute montage, and an epilogue reveals that the Pashtun villagers agreed to help Luttrell as part of a traditional code of honor known as the Pashtunwali.