Previously, the aliens that were trolling the kids revealed that they played the same game and failed somehow. Act 5 begins with a prequel telling how the trolls from Alternia played their own session.

It is Karkat Vantas’s sixth wriggling day and he is just as crabby as ever. His friend Sollux Captor invites him to play the computer game Sgrub, which Sollux wrote by parsing the hieroglyphic code from the mystic ruins their friend Aradia Megido discovered in a cave.

Sgrub, like Sburb, is the gateway to the Medium. Each game session has its own incipisphere containing a Skaia, Prospit, Derse, individualized planets for the players, frog temple borne by the reckoning, and so on. Alternia has two sets of ruins, one red and one blue, so Sollux organizes his friends into two teams.

Sollux prepares to lead Blue Team with Aradia while Karkat assumes command of Red Team, connecting to his friend Terezi Pyrope. Looking for teammates, Red Team recruits Gamzee Makara, Tavros Nitram, and Kanaya Maryam. They also ask Nepeta Leijon, but her moirail Equius Zahhak makes her join Blue Team instead.

Moirallegiance is one of four acknowledged types of troll romance called “quadrants,” each with its own symbol:

• Moirails, in the diamonds quadrant, are pacifying soulmates.
• Matesprits, in the hearts quadrant, are reproductive lovers.
• Kismeses, in the spades quadrant, are reproductive haters.
• Auspistices, in the clubs quadrant, are caring mediators.

When Aradia admits that the game will doom Alternia, not save it, Sollux tries to call the whole thing off. He succeeds only in goading Karkat into running a computer virus that curses his friends to lose their animal guardians known as lusus naturae. They all prototype their dead lusus before entering, except for Aradia. After putting Sollux to sleep to make him the last player to enter, Aradia connects to Nepeta and prototypes her own kernel with the frog head icon from the ruins.

What happens next has a bit of backstory.

Some of the trolls used to play a live action game called Flarp. Aradia and Tavros were larping against Terezi and her teammate Vriska Serket when Vriska used psychic suggestion to make Tavros jump off a cliff. The fall made him paraplegic.

Aradia retaliated by summoning ghosts to haunt Vriska. Vriska retaliated by making Sollux kill Aradia. Terezi retaliated by making Vriska’s oracular magic cue ball explode in her face, taking an arm and an eye. Vriska retaliated by hijacking Tavros’s psychic animal communion with Terezi’s unborn dragon lusus to make Terezi stare into Alternia’s sun, blinding her.

After that, Terezi and Vriska made a truce. Terezi’s dragon taught her to see with her chemical senses, while Vriska’s neighbour Equius built her a prosthetic arm. Aradia stuck around as a ghost, communing with the voices of the dead, which guided her in orchestrating the launch of Sgrub.

Hoping to lead Blue Team, Vriska asks Equius to make a gift for Aradia, a mechanical body that will house her ghost. But after constructing the soulbot, Equius connects to Aradia and delivers it himself, doublecrossing Vriska and shutting her out of Blue Team. Vriska connects to Tavros and Kanaya instead.

In the Land of Pulse and Haze, Karkat meets the Jack Noir of his session, who offers to help him usurp the Black Queen. Red Team aggressively executes the plan, ultimately exiling both Jack and the Queen to post-reckoning Alternia, where they become a Scurrilous Straggler and a Banished Quasiroyal. Later on, Jack would take the name Spades Slick and form the Midnight Crew with his fellow exiles, while the Quasiroyal would join their rivals The Felt as Snowman.

As their entry chains near completion, Red and Blue Teams begin to see signs of each other’s presence. They discover that they are sharing a single twelve-player session, not two separate sessions as they thought. Red Team prove to be the session’s Prospit dreamers and Blue Team the Derse dreamers, with two exceptions. Aradia does not seem to have a living dreamself while Sollux has two, one on Prospit and one on Derse. During Sollux’s long sleep, his Prospit dreamer wakes. After recovering from a taste of mind honey, he connects to Karkat while Kanaya connects to Equius, completing the Mobius Double Reacharound that is their entry chain.

Kanaya has known about the impending galaxy-wide extinction of her race for a long time. Waking young on Prospit, she saw Rose’s walkthrough in a cloud vision. When her mother grub lusus dies, Kanaya pulls from its carcass a horny orb that she hopes will resurrect trolldom.

The doom of the troll species and their interstellar empire is an event called the Vast Glub. The sea princess Feferi Peixes’s lusus is Gl’bgolyb, a squiddly terror of the deep. In its dying throes, Gl’bgolyb makes a terrible psychic shriek that kills every one of the Empress’s subjects, including Sollux before he makes it into the Medium. Feferi comes to his rescue, waking his Derse dreamself with a corpsesmooch. This comes to be recognized as one of the game’s resurrection mechanisms.

In his effort to unite the two teams, Karkat discovers a chat client feature that lets him create memos which exist outside the flow of time. He and his teammates can read a memo before it is written and write in it after having read it, allowing (and compelling) them to talk to him from the past and future of the session. The others use this new mode of communication mostly to air their relationship problems. Karkat responds with an unending stream of cantankerous hectoring, much of it directed at himself.

The trolls’ session continues for about a month, but for us readers it all goes by in a blur. They circle the Medium killing monsters, finding treasure, exiling agents, and sometimes dueling. Sollux fights Feferi’s fellow seadweller Eridan Ampora. Aradia in her soulbot fights and fatally wounds Vriska. Then, having made her pay, Aradia time travels straight to the end of the game. Vriska recovers somehow.

The Black King, made vast and powerful by Gl’bgolyb’s prototyping, initiates the Reckoning and sets himself up as the endgame boss. Thousands of sacrificial Aradias arrive from doomed timelines to join the twelve heroes in the final fight. Everyone works together to slay the King.

At the end of their ordeal, the trolls are presented with a door to a new universe that was to be the ultimate reward. But before they can react, an invincible demon appears, destroys the door, and shreds all but one of the Aradiabots. Narrowly escaping the demon’s wrath, the trolls hunker down in an ectobiology meteor in the Veil, stuck between universes.