The game starts in January 1967 in Saigon, South Vietnam. A CH-47 Chinook containing the player, Caleb Walker , and other G.I.s, lands at Tan Son Nhut Air Base in southern Saigon. Walker, along with his squad mate, Private Kowalski, are chosen by a CO to participate in an air assault on a Viet Cong encampment within Kon Tum province. Walker and Kowalski are put under the command of Lieutenant O'Brien along with another G.I. nicknamed Short Timer. As Walker and his squad proceed through the area, a friendly fire incident, involving flawed mortar coordinates, forces another G.I. named Tomkins, to join the squad. Along with the help of a special operations squad, led by a Sergeant Ramirez, Walker and the others clear out the VC encampment. The encampment is soon after converted to a firebase which serves as a head quarters for Walker and his unit.
Soon after, Walker's squad is tasked with investigating VC activity in a nearby village. The squad is also charged with finding a journalist who had recently gone missing in the village. After learning about the dangers of booby traps, the squad then proceeds to the village. However, it becomes very clear that the villagers are aiding the VC when the squad is ambushed in the rice paddies just outside the village. After clearing out the VC, Walker begins the task of searching for weapon caches within the village. After finding numerous hidden weapons and supplies, the squad begins searching for the missing journalist, and shortly thereafter find him being held hostage by several VC. They jumped to the next task of seizing an old French fort and defend it from the Viet Cong. As the game progresses, the group members began to die one by one in various missions to come. New soldiers are later introduced and Walker joins special forces. They take on subversive, rescue, and assault missions. Cal's final mission is to defeat General Diem, the game's main antagonist. He succeeded and delivered the General Diem's severed head to the base.
The game ends with only Walker and another South Vietnamese Army soldier named Monty with the rest of the squad dead following a massive joint NVA and VC attack on the Kontum. Walker ends his tour of duty and continues a second tour of duty with his own special operations squad
Shellshock: Nam '67 sold over 900,000 copies.