Many Inklings gather in Inkopolis Square near Inkopolis to partake in Turf War battles, which are more popular than ever.
A new trend hits Inkopolis Square: part-time Salmon Run gigs where you hunt for Golden Eggs for a mysterious employer named Grizzco Industries.
Meanwhile, the Great Zapfish disappears again. This time, Callie from Squid Sisters also goes missing.
Trouble is brewing for the Inkling world, but Cap'n Cuttlefish and Agent 3 aren't around to see it, instead patrolling the far reaches of Octo Valley. Marie is living a quiet life alone in Octo Canyon, an underground world that can be reached via a manhole in Inkopolis Square. She recruits a young Inkling to be Agent 4 of the New Squidbeak Splatoon, filling them in on the mission at hand.
Agent 4 searches Octo Canyon for the Zapfish and the Great Zapfish. After clashing with the Octarian army, Agent 4 goes up against DJ Octavio, the mastermind behind all the trouble.
A brainwashed Callie tries to stop Agent 4, but Sheldon and Marie are able to restore her memory. Together, they're all able to defeat DJ Octavio.
The Great Zapfish is once again returned to Inkopolis Square, and Inkling peace is restored with little to no fanfare.