The SAS is the character players will play as. The SAS character has appeared in all SAS games made.
For SAS 1, the player will act as a lone operative whose orders are to eliminate all zombies in the area.
A 3D version of the first game. It follows the same storyline of the normal Zombie Assault, but just in a 3rd person 3D view.
For SAS 2, the player will resume the role of a SAS operative, similar to the first game. The objective remains the same, this time in a military base.
For the expansion, the player is the same from the previous game, with the same objectives as usual. For the Expansion part, the map layout is an Asylum.
For the third game, the player again plays as a SAS operative. The SAS Soldiers are sent into a rural area after receiving repeated reports of zombie attacks in that area. As they were staging in a farmhouse, they became under attack by a horde of zombies. After the SAS Soldiers finished killing the zombies, they are sent to an airport to eradicate the zombies there. Later, the Soldiers travel to a nearby carnival, where they are ambushed by the zombies. When the SAS finished killing all the zombies in that area, they were taken to an abandoned village where zombies spawned from sewer holes. The SAS then eradicates the zombies and finds a trail of bodies to a village. Intel says that the village is ground zero. However, upon finding intel regarding the outbreak, the SAS realized that the village was merely a test site. Ground zero happens to be an isle off the coast of Britain. The Soldiers enter the isle and began to kill the zombies in there. After finishing killing off the zombies, they destroy the castle. The SAS later evacuate in a helicopter from the isle, followed by flames. This concludes the main part of the game, with the story being expanded in the mobile version.
The SAS team begins by defending a shuttle which is stuck in an infected space station while the pilot fixes the ramp doors. After about six minutes, the team faces a mutated zombie(s). As soon as the zombie is eviscerated, the team leaves the Kurios station.
Meanwhile, as the team is gearing up for their next mission, an intel officer order the men to collect a vaccine found on Thera by Combot, their AI regarding the defense of the Federation. However, the president address to the public is also a signal for a Jolt Ship to launch their nuclear missile to destroy Thera. As a result, the SAS has less than 15 minutes to retrieve the Vaccine and get on the Dropship. A few moments after the SAS Team leaves, the Jolt Ship destroys the planet.
Later on Aartis, Combot receives transmission of a SOS coming from a heavily populated city. The team is then sent to the city and eradicate all zombies on site. Also, if any civilian are infected, they are to be shot on site. After rescuing the civilians, the SAS fight a mob of zombies and a boss zombie(s).
The SAS are then informed that Combot has been compromised. With that said, the team are sent to a market where they encounter purge nests. Also, while on the mission, one of the SAS says how there's still twinkies. Soon after destroying the nest, the team encounters five pods in the parking lot. Regardless of whether the team destroy all the minion pod, remaining pods suddenly explode and releases all the zombies found inside.
Soon after, the team is then sent to a mansion where a VIP is located. The team objective is to retrieve the VIP and evacuate the area alive. The team enters the mansion and kills any zombies found inside. When the team finds the VIP, the operatives seemingly starts to regret rescuing the VIP. When a operative acquires any loot with the VIP with them, the VIP will say that the loot belong to him, resulting in the operative ready to shoot the man down. While fighting the zombies, the VIP notes that his robotic servants are acting weird. After the robotic servants are destroyed, a helicopter arrives to evacuate the VIP and the SAS.
After evacuating the whiny VIP, the team are sent to an underground building, to reactivate power to a Hospital. While the SAS was activating the power, they had found 3 dead SAS Soldiers. It is unknown whether those 3 soldiers died by the infection or got killed by Combot. During the Mission, the power activated automatic turrets, Zombdroids and Loaderbots.
Although power is back online, Aartis is nearly over run by the zombies, the team has to evacuate the planet. A swarm of zombies were swarming the place - there was no time to barricade the entire city. As a result, the SAS Team fights against multiple waves of zombies without letting more than 25 zombies get past them. Finally, the Helicopter arrives to evacuate the civilans and the SAS Team.
Following the successful evacuation of Aartis, reports came in of another outbreak, this one on the icy mining colony of Boreas. Unwilling to take chances, the government sends mercenaries from HVM to assist the locals before sending the SAS in. However, it seems that the mercenaries (or potentially HVM) have ulterior motives, for after helping the SAS protect survivors from the zombies, the mercenaries murder the survivors and attempt to kill the SAS team, stating that "there can be no witnesses." After killing the mercenaries, the SAS squad evacuates by truck. Defending the truck from the incoming zombies, the SAS helped the driver by blowing up vehicles that blocked their path. Momentarily foiled by a collapsed building blocking the road, a member of the team pointed out an alternate route. This route worked - to a point, when an avalanche demolished the truck, presumably killing the driver and depositing the team into the middle of a horde of zombies and the abomination that led them. After a tough fight, the team emerges victorious.
Following the incident, the SAS team receives information of a malfunctioning nuclear power plant. They enter and have to manually power off 3 reactors, each in less than 5 minutes. The plant's door system has gone haywire and zombies are spawning from the floors trying to prevent the team from saving the planet from fallout. After the reactors are powered down and the main computer is restarted, a boss fight ensues as they try to kill the soldier. When the zombies are all dead, the team emerges victorious after a 20-second countdown.