Your name is Chell and GLaDOS (Genetic Lifeform and Disk Operating System) is a Computer AI that monitors, directs and misleads you in a kind of twisted experiment. You must rely on information from GLaDOS to survive as you navigate through a series of mostly doorless rooms using the Aperture Science Handheld Portal Device ("portal gun"). The portal gun creates two portal ends, both of which are simultaneously a potential entrance and exit. Objects, alive or otherwise, that travel through one end will exit the other at the same speed. Also, portals create a visual and physical connection between two different locations in 3D space. Their ends are restricted to planar surfaces, but if the portal ends are on nonparallel planes, bizarre twists in geometry and gravity can occur as you are immediately reoriented to be upright with respect to gravity after leaving a portal. You can pass through open portals at will, but barriers, known as "Material Emancipation Grids" or 'fizzlers' prevent you from carrying objects beyond them. Luckily certain objects, known as 'companion cubes' can be tossed through. Passage through these fields also closes any open portals, so it's important to look before you leap. It's your challenge to survive the hazards of the portals, including booby traps, hidden gun turrets and the treachery of GLaDOS in the search for eventual freedom.