On September 11, 2001, Port Authority police officers John McLoughlin and Will Jimeno, who are patrolling the Port Authority Bus Terminal in Midtown Manhattan, see a plane fly dangerously low overhead. As all of the police officers return to the station, they take a glimpse at the TV, and find that the North Tower of the World Trade Center has been hit by a plane. Sergeant McLoughlin assigns many of the officers to assist in an evacuation attempt of the (still undamaged) South Tower, and they board a commandeered Metropolitan Transit Authority bus. On the bus, they hear reports that the South Tower has also been hit.
When they arrive at the site of the World Trade Center, they realize the extent of the disaster and see one of the first victims to jump out of the towers to certain death. As Jimeno drops off their police equipment in 5 World Trade Center, officers proceed to get safety equipment and enter the concourse between the towers. The group consists of McLoughlin, Jimeno, Dominick Pezzulo, and Antonio Rodrigues. An officer named Chris Amoroso appears to inform them of other events, such as the attack on the Pentagon and the second plane's hit on the South Tower, though the group does not accept this. As the men prepare to enter the North Tower, the buildings begin to rumble. McLoughlin realizes that the South Tower is collapsing onto them and that their only chance of survival is to run into the service elevator shaft. Chris trips and does not have time to get up. Rodrigues is unable to get to the shaft in time. McLoughlin, Jimeno and Pezzulo manage to escape the huge amounts of dust and rubble flying down from the South Tower. However, as the rubble continues to crush the elevator shaft, the three are trapped.
As the cascade of debris subsides, Pezzulo realizes he can free himself and manages to move nearer to Jimeno who, along with McLoughlin, is pinned under rubble and cannot move. Pezzulo tries but fails to shift the debris covering Jimeno's legs and is told by McLoughlin not to leave. As Pezzulo becomes optimistic that they will live, the rumbling begins again as the North Tower starts to collapse as well. Although Jimeno and McLoughlin are not further harmed, Pezzulo is fatally wounded. After he fires a gun through a gap in the rubble to try to alert rescuers to their position, he dies.
Jimeno and McLoughlin spend hours under the rubble, in pain but exchanging personal information. McLoughlin is particularly anxious to keep Jimeno from falling asleep, and Jimeno also realizes that by straining to grab a metal bar above his body, he can make a noise that rescuers might hear. Two United States Marines, Dave Karnes and Marine Sergeant Thomas, who are searching for survivors in the rubble of what was once the World Trade Center, do hear it and find the men, calling for help to dig them out.
Jimeno is rescued first, and then hours later McLoughlin is lifted out of the debris, barely alive. They are then both reunited with their distraught families at the hospital.