Stop the train
Semper Fidelis is the first playable level in Battlefield 3.
A frantic escapee runs through the streets to avoid an unknown assailant. Police sirens fill the night; whoever is pursuing this unknown man is closing in. The character comes to an overpass where a train is roaring by. After a moment's hesitation, the man leaps on-top of the speeding train.
The character breaches through windows and incapacitates an unsuspecting enemy. After taking out a handful of sidearm wielding enemies, a man is heard on the loudspeakers. "My brothers. You know what must be done. no one in this vile place is innocent, no one! Everything and everyone will burn!" The player grabs an M1014 that's being used to jam the door, and proceeds to the next train car. An enemy tries to engage the player in hand to hand combat, but is thrown out the window.
A mysterious man in the suit is seen staring at the character on the next train car. Using his vast intuition, the character climbs out of the speeding train in attempt to circumvent the locked door, but notices C4 attached to the train's connections. Barely managing avoid the explosion, the player attempts to climb through the window. The mysterious man shoots at the player. Luckily, the mysterious man misses, and the character climbs on the train roof. After fending off enemies also clambering to the top, another explosion is seen near the front of the train. The character jumps through a conveniently placed hole in the ceiling and takes out another group of enemies.
As the player gets closer and closer to the front of the train, the enemies' objective become obvious. The train is wired full of explosives.