*CUT TO THE CHASE*
NOTE: This spoiler was submitted by Emilio
The film opens with a group of illegal immigrants riding in the back seat of a truck. They are driving towards America when the truck breaks down. The drivers get out of the truck, pop open the hood and look at the engine. They don't seem to know what is wrong with the engine. They go to the back of the truck to speak to the immigrants. They ask if any of them are mechanics. A man, Moises (Gael Garcia Bernal) says he is and he gets out from the back of the truck. He walks over to the front of the truck to look at the engine, but he isn't able to fix it. So, the drivers tell all the immigrants to get out of the truck. They proceed to do so. The drivers point the immigrants towards America. They being walking across the desert towards America.
Meanwhile, a man named Sam (Jeffrey Dean Morgan) is driving along a road with his dog, Tracker. They stop, and Sam goes hunting for rabbits. He is able to shoot a rabbit with his sniper rifle. The gunshot alerts the immigrants. They begin running and take cover in a field scattered with cacti and tumbleweeds. After they don't appear to see anything, they stop for a break. Moises notices one of the immigrant men trying to make a pass at a female immigrant, Adela (Alondra Hidalgo). Noticing that Adela is getting increasingly uncomfortable at the man's passes, Moises is able to distract him and stops him from going any further.
Elsewhere, Sam is again driving along the road when he comes across a border patrol agent. The agent asks Sam if he has a permit. Sam asks him if he needs a permit to hunt rabbits. The agent says that he doesn't. Sam tells the agent that he reported earlier about some illegal immigrant tracks that he saw, and he asks the agent if he checked it out. The agent says he hasn't heard anything about it. Sam says "course not" to himself. The agent tells Sam, "Good luck on your hunt," but Sam tells the agent to keep that good luck to himself. Both men get into their trucks and drive away.
Sam comes across the tracks again. He grabs his rifle and goes to look. He calls Tracker over to sniff the tracks, then tells him to go find them. Tracker takes off after them. At this point, the group has split off into two separate groups. One group is far ahead of the other. Moises and Adela are in the group that has lagged behind. However, Moises and his group spot Sam and Tracker from up on a hill. One man in Moises' group asks Moises if Sam is a cop/border patrol, to which Moises replies "no."
Sam spots the group that is ahead. He tells Tracker to go back to the truck. Sam also goes back to the truck to grabs his sniper rifle. He goes and proceeds to kill all of the immigrants in that group, one by one, including the man who was earlier harassing Adela. After killing them all, Sam says "Welcome to the Land of the Free."
Moises' group takes off in the opposite direction. Sam gets back into his truck and proceeds to cheer to himself. Tracker starts barking at the direction that Moises and his group was heading. Sam grabs his sniper rifle and looks in that direction, barely spotting Moises and the group heading over a hill. Sam and Tracker get back into the truck and begin driving in that direction. Sam comes to where the road ends. He gets out of the truck and tells Tracker to go find them. Sam follows on foot behind Tracker. Moises and his group are still running, knowing that Sam & Tracker aren't too far behind.
Tracker catches up to one immigrant man, who is falling way behind. Tracker tackles him to the ground. Seeing this, Adela tries to help the man, but Moises stops her from doing so, knowing it is too late. Tracker proceeds to violently rip the man's throat out. After doing so, he takes off after the other immigrants. The remaining four immigrants begin climbing a rock mountain, desperately trying to lose Tracker. Tracker begins to climb as high as he can go, but only makes it partially up the mountain. He heads back and looks for another way up.
Sam climbs another rock mountain and is able to get a view on Moises & his group. Tracker finds another way up the mountain. Moises and his group come to a point where they have to jump from one rock to another. Moises, Adela, and another immigrant man all make the jump, but the fourth immigrant is hesitant to jump. He takes his time trying to make it over, but when he spots Tracker behind him, he makes the jump. He doesn't successfully make it but is able to hold on to the rock. Moises tries to pull him up, but Sam fatally shoots the man with his rifle. He takes a shot at Moises, but misses.
Sam goes back to the truck with Tracker. He looks at a map and tells Tracker to go do his thing. Tracker takes off after the final three immigrants. Sam gets back into his truck and begins driving. He comes to a canyon and stops the truck. He begins looking at his map again. Moises, Adela and the the third immigrant spot Sam in his truck, around the corner, but Sam doesn't see them because they are hiding in the canyon. Moises and the other two, go back the other way. Sam gets out of the truck and begins walking towards the direction that Moises and his group were heading. Moises and the group spot Tracker in front of them.
They proceed to climb the canyon, desperately trying to get away from Tracker. It works, but Tracker alerts Sam. Sam begins to climb the canyon after them. The third immigrant, falling behind, spots Sam approaching behind him. Sam grabs his rifle to shoot the man, but the man loses his grip and falls several stories to the ground below. Moises and Adela hide in the rocks of the canyon. Tracker runs over and begins biting the man. Sam calls Tracker off of him. Afterward, Sam shoots the man in the head, killing him. Still hiding in the rocks, a teddy bear in Moises' backpack begins going off. Despite his attempts to silence it, it alerts Sam to their presence. Since it is almost dark, Sam tells Tracker that he will get them tomorrow. The sun sets for the night.
The next day, Adela tries to look for Sam & Tracker's whereabouts. She spots Sam's truck from the top of a hill. She narrowly avoids getting bitten by snakes. Tracker senses her presence from the truck, so he takes off after her. Sam follows behind him. They get to the top of the hill and hear the teddy bear again. They find the teddy bear in a pit of snakes. It is a distraction as Moises & Adela make their way to Sam's truck. As Sam attempts to shoot them, he is graced by a snake, which he shoots. Moises and Adela make it to Sam's truck, avoiding his bullets. Moises grabs the antenna on Sam's truck and uses it to open the front door. They get into the truck, narrowly avoiding Tracker. Tracker begins to climb onto the truck. Moises is able to hot-wire the truck and takes off.
Moises and Adela are happy that they have gotten away. However, Sam shoots at the truck, hitting Adela in the shoulder. This distracts Moises, and he ends up flipping the truck over. Moises climbs out of the truck and spots Sam climbing down a hill in the distance. Moises pulls Adela out of the truck. He also grabs a first aid kit that was in Sam's truck. Moises and Adela begin walking. Tracker takes off with Sam following behind him.
Moises and Adela take shelter underneath a large cactus. Moises looks in the first aid kit and finds a flare gun inside it, along with some bandages. He uses the bandages on Adela. He takes the flare gun and leaves Adela by the cactus. Sam and Tracker begin to close in on Adela by the cactus. But, Moises uses his flare gun. Sam and Tracker take off after Moises because Sam thinks Adela probably doesn't have long to live (not knowing that she has got medical supplies from his first aid kit).
Moises makes it to a cactus field and begins crossing it. Tracker also crosses through it. Moises stops and loads the flare gun with a second flare. As Tracker gets close, Moises shoots Tracker in the mouth with the flare. Sam, hearing Tracker's cries, runs towards him. He is too late as Tracker is dying. He shoots Tracker in a mercy kill and begins crying, saying that he's sorry. This further angers Sam and he begins shouting to Moises that he's a dead man.
Moises spots a border patrol vehicle in the distance. He shouts at it but is not able to signal it in time. Sam spots Moises and shoots at him, but since Moises is right near a cactus tree, Sam hits the cactus tree. Moises takes off and Sam shoots at him again and misses a second time. Moises begins climbing another rock hill, avoiding a couple more shots from Sam. This leads to a five-minute cat-and-mouse sequence as Moises tries to escape from Sam at the top of this one massive rock mountain. Moises continually hides from Sam, until Sam stops at the edge of one of the cliffs of the mountain. Sam looks around for any signs of Moises. Sneaking up behind him, Moises tackles Sam off the mountain. Both men hit the side of the mountain and roll down it.
Sam is injured. He looks down at his leg and sees that the bone on his right leg is sticking out through the skin. However, Moises appears to be fine. Both look over and see Sam's sniper rifle about twenty feet away from both of them. Both men get up and attempt to run to it. Moises is able to get the rifle. Sam pleads with Moises for his life. Moises chooses not to shoot Sam, but decides to leave Sam to die in the desert, despite Sam's pleas for Moises not to leave him.
Moises begins walking again. He walks back to where he left Adela. He gets her to her feet and walks with her on his back. He carries her for miles, throughout the rest of the day. As it begins to get dark, Moises notices some lights ahead from some shacks and/or buildings, implying that they are near a town. The camera pans across the desert as the credits roll.