Description
A zombie apocalypse has ravaged the entire world, with zombies outnumbering humans 400,000 to 1. The surviving humans live in security within barricaded camps and secure underground bunkers.
In an underground facility in the Everglades housing scientists and soldiers, the scientists are trying to find a solution to the zombie pandemic; the soldiers have been assigned to protect them. Dr. Sarah Bowman, her lover and soldier Private Miguel Salazar, radio operator Bill McDermott, and helicopter pilot John fly from their underground base to Fort Myers, Florida, in an attempt to locate additional survivors. They find only a large horde of the undead, and they return to the base, where they are told that the military detachment's officer-in-charge Major Cooper has died. Sarah becomes concerned over Miguel's worsening mental state.
Dr. Logan, the lead scientist (whom the soldiers nickname "Frankenstein" because of his grisly surgical dissections of zombies), believes that the zombies can be made docile by training and conditioning. He keeps a collection of captive zombies for use as test subjects, in a large underground corral in the compound. The angry and reactionary Captain Rhodes and the soldiers that he leads vehemently object to the dangers involved in capturing zombies and keeping them inside the compound. The tension between soldiers and scientists worsens in the face of dwindling supplies, loss of communication with other survivors, and slow, uncertain progress in research.
During a meeting between the scientists and the soldiers, Rhodes declares that, following the death of Major Cooper, he is taking command of the base. He only grants the scientists "some" time to prove results, and declares that he will execute anyone who interferes with his leadership. He also threatens to abandon the scientists and leave the compound, cutting off their protection from the zombies. Shaken by Rhodes' threats, Sarah goes to the quarters shared by John and Bill to discuss the situation. John professes his conviction that the zombie-plague is a form of divine punishment against mankind, that the scientific mission is doomed to failure, and that the effort to preserve records of civilization is pointless. He suggests that the three of them should take the helicopter, abandon the soldiers, and fly to a desert island somewhere where they could live off the land and start a family.
Dr. Logan hopes to secure Rhodes' goodwill by showing him the results of his research. Logan is especially proud of "Bub", a friendly and non-aggressive zombie who remembers some parts of his past life and engages in rudimentary human behavior: listening to music, aiming a pistol, saluting Captain Rhodes, and repeating a string of garbled words. "Civility must be rewarded," Logan tells Rhodes. "If it's not rewarded, there's no use for it." Rhodes, however, is not impressed.
During a zombie roundup mission, a zombie escapes his harness when Miguel loses his focus, and the zombie fatally wounds Sergeant Miller, who fires his gun with his dying breath and accidentally shoots and kills a friendly soldier named Johnson. Miguel attempts to kill the creature, but another zombie bites him on the arm. Sarah amputates the arm and cauterizes it with fire to stop the spreading infection from killing Miguel and re-animating him into a zombie. Rhodes then calls off the experiments and demands that all captive zombies be destroyed, as well as severing any further help from him and his remaining men.
Sarah and Fisher later discover that Logan had been experimenting on the remains of the dead soldiers and an audio recording of him rambling to himself. Fearing that Logan has gone insane and with the conditions worsening, Bill decides that they should leave in the helicopter immediately. Rhodes finds out that Logan has been feeding the flesh of his dead soldiers to Bub as a reward for his docility and positive behavior. Enraged, Rhodes kills Logan and seizes the remaining scientists and non-military personnel, stripping them of their weapons. Rhodes brings his prisoners and attempts to force John to fly him and his remaining soldiers away from the base, which John refuses to do. In response, Rhodes kills Fisher, locks Sarah and Bill inside the zombie corral with the zombies, and orders Steel to beat John into submission.
Back in Dr. Logan's laboratory, Bub manages to escape from his chains and finds Dr. Logan's corpse. In a display of human emotion, he mourns the loss of his instructor, then picks up a pistol and goes in search of revenge.
Meanwhile, a suicidal Miguel heads off unnoticed to the outside fence, where he first opens the gate to allow hundreds of zombies to walk through, and then allows the zombies to begin tearing him apart before he presses the release button that lowers the steel loading gate and gives the zombies access to the base. While he is doing this, John overcomes his captors, steals their weapons and goes into the zombie corral to rescue Sarah and Bill. As the zombies enter the complex, Rhodes leaves his men to be killed by the zombies and flees. Bub finds Rhodes and fires at him. Rhodes hastily tries to escape, but he runs into a huge mass of zombies, and is shot in the stomach by Bub. Bub sarcastically salutes Rhodes, who is then torn apart by the zombies. John, Sarah and Bill manage to get to the surface and fly in the helicopter to a deserted island, as John had earlier suggested.
