Miguel is one of many soldiers assigned to the bunker to protect and aid the scientists trying to reverse the infection process which has turned most of humanity into flesh-eating zombies and is in an unsteady relationship with the bunker's only woman, Sarah. However, the lack of outside contact, and being surrounded by the undead both above and below is taking its toll on his well-being. At the beginning of the movie, he is close to breaking point, almost dropping the pole to hold zombies back while the survivors capture them for Dr. Logan's research, yet refusing any help or drugs from Sarah to calm him down. When tasked with helping to capture more zombies, the pole breaks and one of the captured zombies breaks free, biting Miller. Miguel attacks the second captured zombie in a frenzy and is also bitten. He snaps and runs into the vehicle storage area, consumed by fear and his own madness. Sarah knocks him out however and proceeds to amputate his bitten arm, with the help of her allies, Bill and John, stopping the infection from spreading, though Captain Rhodes and Steel are convinced he will die and reanimate.
Miguel does survive, and is watched over by Bill and John, but makes his way towards the elevator unnoticed as order breaks down within the bunker. Despairing and unhinged, he removes the elevator controls and heads towards the edge of the compound to face the zombie horde. He unlocks the gate and flees as the undead begin to swarm in. Miguel then straps himself onto the elevator platform with a control pad in hand and is almost immediately devoured by the zombies while he presses the button to lower the elevator, now full of zombies, into the bunker, sealing the survivors' fate.