ech, due for full 100% revamp... later
Chapter 1: Return to Aperture
Chapter 2: Her Again
Chapter 3: Retesting
Chapter 4: Sabotage
Chapter 5: The Depths
Chapter 6: West Wing
Chapter 7: The Summoning
Chapter 8: Nanobots
Chapter 9: Guidance
Chapter 10: Finale
Portal 5 Co-op has 16 courses. The first 12 are playable at any time, and are preunlocked, but 13 is unlocked after all 12 other courses are completed, and 14 is unlocked by completing 13, then so on.
Course 1: Cubes and Buttons
Course 2: Flinging
Course 3: Energy Pellets
Course 4: Crushers
Course 5: Faith Plates
Course 6: Deadly Lasers
Course 7: Bridges and Funnels
Course 8: Platforms
Course 9: Gels
Course 10: Vents
Course 11: Turrets
Course 12: Plasmatic Spheres
Course 13: Timed Tests
Course 14: Overgrown
Course 15: Malfunction
Course 16: Neurotoxin
Portal 5 starts off with Cave Johnson(who has memory loss and is almost certainly a clone) sending Test Subject 1-2076 down to the surface of Earth, back to the original Aperture Science. He tells you to reclaim the center, and stuffs you into an escape pod-like object. You fly down to Earth and land in the old facility. You walk towards a voice. It turns out to be a core. He introduces himself as Machiavelli. He expresses his gratitude that a human was there, and asks you to help him escape, and he would do the same. He then tries to open a passageway, fails, and tries going another way, the "long way". You travel through several test chambers, and also travel through Samaritan's area. Samaritan is another Gen II core who is tasked with taking care of the Class III Cores. Mac shows that he hates Sam, and Sam tells you that some of his cores are gone. You must go through 4 chambers involving Pneumatic Diversity Vents and retrieve Samaritan's Class III Cores. Then Mac leads you to a catwalk system, where GLaDOS discovers your presence, but as the surveillance system is malfunctioning, she does not know who you are. She drops you into a tube that leads to her chamber.
She reacts very strongly at seeing you, and of course can't believe it. So she gives you a DNA test and discovers, through slight discrepancies, that you are a clone. She then puts you back into testing. You must complete 7 chambers, and Mac doesn't appear until the fifth. He only appears one other time, at the end of the chapter, and tells you that he's working on getting you out. however, the next chapter starts, and still 9 more chambers must be completed until you escape. Then Mac finally busts you out at the tenth chamber. The chambers revolve around Magnets and Plasmatic Spheres.
You go through many catwalks and hidden areas, and destroy several "tank rooms". After 6 or so of these are destroyed, Mac takes you to the region known as The Crush, which is a dangerous area of pistons and crushers, which, in reality, is a giant engine sort of device. It converts electrical energy to kinetic energy, then back to electrical energy, in a classic case of Aperture's wasting of energy and time. Within the center of The Crush is a region known as Generator Six, which you must destroy. Once it is destroyed, instead of removing power from GLaDOS Chamber, it destroys the rest of The Crush, and sends you plummeting to the Old Aperture facility. Mac can speak to you through speakers occasionally, though mostly you're on your own.
You find yourself in a test shaft from the late days of Cave Johnson. This test shaft includes the testing of Adhesion Gel, original gels, and a new gel, the original Ditto Gel, which clones objects. Afterwards, you find yourself in a place Mac calls "The Nodes". These nodes are the gel manufacturing facilities within all of Aperture. Mac says that he would tell you to destroy them, but he wouldn't know how to destroy them. Instead, he says to solve the chambers near the Nodes and to use the elevated nodes to escape Old Aperture. Once you reach the uppermost node, you reach the operational elevator and escape. However, this elevator brings you to the disused West Wing of Aperture instead of the main, pre-explored region.
The test chambers here involve Plasmatic Spheres, Magnetic Gel, and Reflection Gel. Then you meet Rose, and she helps you through the next set of chambers involving Rocket Turrets and Nanobots. Then GLaDOS finds you, and discovers the Rockets and Nanobots, things that she had forgotten about through a strange malfunction, and decides to use the elements to increase security. Mac allows you to escape, and he tells you that you need to destroy the Nanobot and Rocket Manufacturing so that it will be easy to defeat GLaDOS.
Once this task has been completed, and when you are running to an area from which Mac says you can escape, you enter an area with a core attached to a robot body with many wires attached, and in a socket on the wall is an odd core with a blue "eye". He chatters wildly, and Mac translates what he says. This core is Iceblue. Mac tells you to move Iceblue to a particular room, and you do so. Once Iceblue is plugged into the socket, the door begins to open, but shuts immediately after you attempt to enter it. After, you are taken to a tube complex, where you must solve several tests to rearrange the tubes to escape, and once the last one is completed, GLaDOS intercepts you, and moves to more tests, involving Portal 1 and 2 elements, as well as Pneumatic Diversity Vents. Then you reach GLaDOS' Chamber and battle her. GLaDOS is disinclined to battle, but she begins to form the opinion that Chell Clone 2076 is more terrible than Chell ever was, and tries to kill her. However, before the battle begins, something awakens from within the facility. This thing is Kyle. Then the ending song(s) play.
There are more gamemodes in this game than any previous game.
Singleplayer Story(12 chapters)
Cooperative Testing Initiative(16 courses)
Advanced Cooperative Testing Initiative(35 chambers)
Commentary Mode(same as singleplayer story)
Battle Mode(25 areas)
Mobility Gel Testing Initiative(_ chambers)
Plasmatic Sphere Testing Initiative(75 chambers)
Perpetual Testing Initiative(infinite chambers)
In Portal 5, Half-Life style weaponry acts as collectibles. These are used in Battle Mode, a new gamemode.