American Warrant Officer "Chief"' Warrens returns to active duty in the war against terrorism in the Middle East and reunites with his old squad, composed of soldiers named Dozer, Ryan, Fox, and Jones, the Captain. After completing a training run, Chief is immediately taken with his squad to an area believed to be being used as a terrorist radio outpost. The squad splits up and travels around the area, destroying a number of radio towers, before regrouping in a Palace. Their extraction chopper is shot down by the terrorists, and so they are forced to defend the Palace from a large number of terrorists before being safely extracted in a Humvee. During the mission, the squad notice how the terrorists seemed to be ready for them and begin to suspect the presence of an informant.

The squad are then sent to a hospital in order to capture Abu Bahaa, a terrorist warlord, who is apparently undergoing an unspecified surgery there at the time. Chief and Dozer infiltrate the hospital through the sewer system below, while Ryan and Jones wait outside. Ryan is killed in this mission. Upon reaching Bahaa's room, Chief finds that they have been tricked; the hospital has been rigged with explosives and a dummy corpse has been placed in Bahaa's hospital bed. However, he and Dozer manage to escape unscathed, while also protecting Jones, who has been wounded.

After Jones recovers, the squad break into a dockyard which Bahaa is using to conceal a nuclear weapon. They discover that the terrorists actually have an enormous base underground, the entrance hidden within a shipping container. Chief is sent in to find the nuke - he encounters Bahaa inside, but is forced to leave him in order to locate the bomb, which could be detonated by the terrorists any minute. He eventually finds the nuke and is able to secure it, while Bahaa flees outside and attempts to escape in a truck. The squad pursue him in a humvee, chasing him out of the dockyard and through a train tunnel, before eventually managing to flip his truck just as he reaches the highway.

The squad find Bahaa lying by the truck, still alive, and Dozer prepares to capture him; however, Jones betrays the squad, killing Dozer and taking Fox hostage. Bahaa taunts Chief, saying that he is weak and that he has no choice but to surrender, but Chief shoots Jones, who falls to the ground with Fox. Bahaa pulls two Fragmentation grenades from his jacket and prepares to blow up both Chief and himself, but Fox pulls him to the ground and tells Chief to run. Chief takes cover by the Humvee as both Bahaa and Fox are consumed by the explosion.

For all of his efforts, Chief is promoted and becomes known as a hero. He travels to Fox's residence and meets his wife, informing her of his act of martyrdom and how he saved his life.

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The game starts with the player taking control of Mustang Squad's Private Newman, who is imprisoned in a prison camp operated by Pablo al-Banni. Newman is questioned by Pablo through a Translator before he is knocked out with a rifle butt to the head. Fellow squadmate Private Downs rescues Newman, and then they attempt to make an escape. After Downs knocks out a guard unaware that the prisoners are free, Newman acquires an NX8 Handgun and later an AK-47, and the two attempt to fight their way out of the compound.

The game then enters a flashback following Lt. "Chief" Warrens, the player's character from Modern Combat: Sandstorm, and Delta Squad. They assault an oil rig in the Middle East to find Khalis Ghazi, who is believed to be a member of the terrorist organization established by Abu Bahaa. The player clears rooms of enemies and fufills various objectives until he is attacked by Ghazi himself, who is promptly disarmed by the player. While they wait for extraction, Ghazi is coerced into revealing his superior's identity.

The player then takes control of Sergeant Anderson, a member of Razor Squad. They escort Azimi, ambassador of an unidentified Middle Eastern country, to the United States embassy using a Humvee The player moves from rooftop to rooftop, eliminating various enemies and the occasional tank, until the Humvee and the player are funneled into a courtyard, where they are ambushed by waves of enemies and tanks.

The player then takes control of a mounted gun on the Humvee they just escorted as they travel to the American Embassy, battling waves of enemies, troop-carrying trucks, and a helicopter.

Next, the player sneaks through a snowy landscape littered with the remains of a wrecked airliner to reach a derelict power plant where Ghazi's boss,Nikitich is hiding. Mustang Squad finds him attepting to flee in a tank and are forced to engage him, resulting in the tank being disabled and Nikitich revealing the location of his superior, Popovich. The squad leads an assault on the Cold War Compound where he is holed up, methodically searching each room in the bunker until Newman and Downs end up confronting him on his Soviet submarine. However, Popovich deftly turns the tables and captures the two, shipping them off to Pablo's jungle compound.

The player then resumes the storyline where they left off after the ambush in the first mission. They flee through the jungle, fighting off Pablo's men as they escape through the ruins. During a brief pause, they contact the rest of Mustang Squad and are directed to an extraction point, where they are picked up in a Huey. The player then takes control of Sgt. Anderson and are ordered to assist in the assault on Pablo's mansion. The player attempts to sneak in, but is discovered and are forced to revert to an all-out assault. The team breaks into Pablo's office, where they find Pablo's translator, who claims he has no loyalty to Pablo and points the player in the direction Pablo ran off in. However, as the player enters the elevator they were led to, a massive explosion throws the player into the elevator's wall, and Rollins is killed. The player is forced to chase Pablo on foot through the local shantytown, fighting off the local militia forces and another Mi-24 Hind, eventually leading to a fistfight with Pablo on his Huey, and ending with the player forcing a grenade into Pablo's mouth and pulling the pin.

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Modern Combat 4: Zero Hour takes place in the year 2037.[1] The game starts when the US send a large army to a summit to secure it. While Page is underway to Hawaii, Corporal Joel Blake arrives at the Red Summit with a small squad of US soldiers, led by Lieutenant James Walker, the protagonist of Fallen Nation. They storm their way through the beach, and receive word that another allied team is pinned down by the SGS Militia. The team make their way to them, and discover that the president of the United States has been taken hostage by Edward Page, the client of SGS.

The game then switches to the perspective of Edward Page (a supporting antagonist from Fallen Nation) two days prior to the invasion of Hawaii, attacking the WCIB in Seattle as a distraction of a large attack on the C3 summit in Hawaii. Saunders Global Security (SGS) is a group of mercenaries who are hired for the security of the summit. After Page and Everett Saunders plant bombs on the WCIB, they are extracted via helicopter, just as the building explodes inches below their feet.

Anderson (a supporting character in Fallen Nation) is dispatched into a devastated Seattle, along with several other AFTER operatives, to head to a police station. Chief (likely Warrens) tells AFTER operatives that terrorists have been spotted all over the city. Making his way to the WCIB, Anderson, along with Caydan Phoenix (the main character of Blackout) rescue the AFTER operatives that were being held hostage by SGS. As Chief tells Anderson that terrorists are using vans to transport hostages, he leaves Cayman Phoenix and the secured hostages, continuing by himself. As Anderson battles his way onto the street dominated by SGS forces, a van screeches from a corner and onto the street. Anderson kills all of the SGS forces, and catches up with the van, largely caved in by debris from a section of the tunnel that has collapsed. An SGS soldier leaps out from behind a piece of fallen debris, and pulls out a knife. However, Anderson retaliates and shoves the knife into the SGS soldier's abdominal hemorrhage. Just before death, a sputtering SGS soldier says that the attack on Seattle was all a distraction for Edward Page to abduct the US President in Hawaii.

The game switches back to the perspective of Edward Page, as he takes the president hostage in the Iakoo Beach Resort. As Page assists other SGS soldiers, he and the SGS soldiers successfully place a bomb inside the resort. Afterwards, Page ruthlessly plants IEDs all around the resort, in an attempt to slow down the pursuing US forces. Phantom Unit pursues Page. While they disarmed the bomb, Page had almost reached his helicopter. Therefore, they were unable to rescue the President.

Intel confirms Everett Saunders (a former US Special Force in the same unit with Page) is somewhere in the city of Barcelona, so Walker, Blake and Lieutenant Downs (a major NPC in Black Pegasus and Fallen Nation) are dispatched to find him and extract information on where Page may have taken the president. They locate Saunders and try to arrest him, but Blake needs to throw him off a balcony to save Walker, and Saunders is thought to be dead.

The team is then sent to the SGS base in South Africa. Upon attacking the base, Blake is knocked out of his helicopter and forced to fight his way through the base alone. He rescues the president and then reunites with Walker and Downs. The president retrieved information indicating that Page is holding up in a base in Antarctica. The team is dispatched, and discover that Page plans to fire a bioweapon capable of killing about 4 billion people, in an effort to "restart" the human race.

Warning: spoiler below. Move cursor to read the text.
After fighting their way through the Antarctic Unified Citizens base and locating a biolab, they realise that the biolab that they are in contains the bioweapon that is capable of killing 4 billion people. Anderson and Blake are ordered to wait for a hazmat team to arrive, however, Anderson disobeys orders. He orders Blake to open the door leading into the room where the bioweapon canisters are. Blake does so, but Anderson pushes Blake off his feet, and rushes into the lab, breaking the electronic lock so no one can enter, and begins planting bombs on the bioweapon canisters. However, Anderson is attacked and stabbed by Page whilst planting the bombs. Before he dies, Anderson tells Blake to detonate the bombs. Blake does so, with the blast killing Anderson and incapacitating Page. When Page regains consciousness, he finds that US soldiers are breaking into the base and are destroying his bioweapon. Realising that he is defeated, an enraged Page fights his way through the base and attacks Downs and Walker, shooting Downs in the arm and fighting with Walker.
Page overpowers Walker and is about to kill him, however, Blake kills Page, and he and Walker assist Downs in fleeing the building before it blows up.

In a post-credits scene, it is revealed that Saunders is alive. He states that he was using Page all along, and that he has already put in motion the first part of a terrorist attack of his own, claiming that soon they "will soon know the true meaning of terror".

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