The story begins in the year 2036, where the world has been overrun with monsters created by a mutant pathogen. At the fictional Chandler University two researchers named Sam Quinn and Mallory Beckett attempt to use an experimental time machine, to go back in time one year to prevent the accident that unleashed the plague.
However, the plan doesn’t work out because the machine deposited them in what appears to be ruined version of their lab. Sam and Mallory soon learned that their time machine transported them to an alternate universe. In this world, Eden, an A.I designed to combat environmental degeneration with nanobots, went insane and triggered a second ice age. Sam and Mallory also learn that their machine gave them the ability to slide between worlds. During their stay in the ice world, Sam and Mallory use their sliding powers to help the citizens of a climate controlled compound with problems like a power outage, a food shortage, a broken water filtration system, and an attack by robots controlled by Eden. They also man a space ship built by the compound’s scientists, to destroy the satellite housing Eden’s CPU.
After destroying Eden, the scientists of the compound offer to use their advance genetics, to cure the mutants of Sam and Mallory’s world. However, the scientists require the data form the experiment that created the mutant plague. After giving the scientists the data, disaster strikes! One of the scientists, a man name Fritz revels himself to a government agent from a world dominated by the Third Reich.
Fritz steals the data on the mutant plague so the Reich can use it to create new bio weapons. Sam and Mallory head to the Nazi world where they team up with a local resistance to regain the plague data and stop the government of the Nazi world’s plans of inter-dimensional conquest.
Unlike many first-person shooters of the era, Quantum Slide does not have a strong emphasis on multiplayer, although cooperative LAN play between up to two people can be selected from the main menu. Instead, the focus is on the approximately ten hour long campaign. In this sense, it was the polar opposite of Quake 3, despite sharing a common engine.
Much of the moment to moment gameplay of Quantum Slide was similar to other shooters of the time. Using a combination of the keyboard and a mouse, players would move their character, either Sam Quinn or Mallory Beckett, in a three-dimensional environment, fighting with a variety of weapons, particularly firearms.
What truly distinguished Quantum Slide was its emphasis on switching dimensions in real time, sometimes mid-fight. At any moment, objects and enemies from alternate dimensions would be outlined in a light blue if they were part of the Ice Age dimension, yellow if they were part of the home dimension, or red if part of the Third Reich Dimension. Players could at any time switch dimensions by pressing the "Enter" key by default, cycling from Home dimension to Ice Dimension to Third Reich Dimension and back to Home dimension.
Objects held by players or in a player's inventory could be carried from one dimension to another. This was key for solving many of the game's puzzles and quests, as well as helping to defeat opponents. For example, before entering a firefight in one dimension, one could carry over a crate to use as cover, or take advantage of slightly different geography of dimensions to get behind an enemy.
The game's basic arsenal included the basic Fist for melee combat, the standard Pistol, the Shotgun, and a Machine Gun. These basic weapons had ammo that could be found anywhere. However, there were also three guns, one earned in each dimension, which can only be replenished using ammo native to their home dimensions. These include the home dimension's "Plague Gun," which deals splash damage over a wide area and can spread between enemies that get too close to each other; the Ice dimension's nanogun, which creates either stable or explosive blocks out of thin air; and the Third Reich dimension's Laser Gun, which can be charged with more ammunition to create a devastating attack.
Each weapon in the game has a non-combat use, be it something as crude as blasting open a locked door, something puzzle-oriented like making blocks to solve a physics puzzle, or igniting an explosive object quickly from afar.