At the dawn of Episode 2 in Invincible's sophomore season, RVJ High School celebrates its graduation ceremony, yet Mark's absence from his designated seat beside Amber, Eve, and William stands out like a sore thumb. Amidst the festivities, Mark engages in a highly anticipated rematch against Doc Seismic atop the Washington Monument. This encounter, however, sees him joined by colossal magma allies, assisting in the battle to obliterate their foe. Despite the monumental landmark sustaining considerable damage, Mark manages to squeeze out a victorious margin. He races back to the ceremony, arriving just as the final chords of pomp and circumstance resonate through the air.
In Eve's whimsical treehouse, the quartet confides in their summer aspirations, with Mark somewhat detached, his thoughts consumed by impending responsibilities. Meanwhile, a NASA-like space force delves into Season 1's Mars mission, where 'sequids' pose a menacing takeover threat. Among them, Astronaut Rus is revealed to be one of these insidious body-snatchers, capable of shape-shifting. Eve expertly navigates city hall's bureaucratic labyrinth, facilitating Chicago's rejuvenation from the aftermath of the Invincible versus Omni-Man clash. Despite her efforts, Debbie fails to alleviate Mark's apprehensions about mirroring his father's fate. Elsewhere, Immortal and Dupli-Kate's burgeoning romance leaves Rex less than thrilled.
Rus, now a sequid, grapples with the nuances of human behavior. Meanwhile, Mark ventures into the eerie Midnight City in pursuit of a rejuvenated Darkwing. To his surprise, Darkwing's mantle has been assumed by his former assistant, who sees fit to banish Mark into a sinister realm known as 'the shadowverse.' Mark, in a moment of intense desperation, traps the new Darkwing alongside him, warning of his untapped potential and the specter of becoming like his father. Debbie lambasts Cecil for his arrangement with Mark, her astonishment doubled upon witnessing Donald, believed deceased at Omni-Man's hands.
Eve discovers her father toiling away at a menial job at 'Burger Mart.' In a gesture of gratitude, she transforms an apple into a glittering 24-karat gold version, only to have her father decline the lavish gift, grounded by humility. Mark attempts to surprise Amber with a special lunch by soaring to Vegas but is hastily summoned into action by Cecil, pulling him back into the thick of adventure.
In the aftermath of Omni-Man's grim deed, where he claimed the life of Aquarus, the rigid customs of Atlantis decreed that Mark must wed Aquarus's widow as a penance for his father's heinous act. Concurrently, the Guardians re-engaged in battle, facing off against the formidable Lizard League. Amidst the fray, Sequid Rus emerged, a superhero possessing the remarkable ability to shape-shift. Unbeknownst to all, Aquaria, Aquarus's widow, was revealed to be the rightful monarch of Atlantis, who promptly abolished the archaic marital traditions. Instead, Mark found himself challenged to a trial by combat, his punishment for his father's transgressions. His adversary, the colossal Depth Dweller, loomed over him, a daunting figure indeed.
Elsewhere, Debbie endured a trying day, attempting to sell a house to a couple dominated by an irate, controlling husband. Her fateful remark, "She's not your pet," led to her premature dismissal. As Mark sought to flee the clutches of the Depth Dweller, he realized he needed reinforcement to escape. But once safe, the beast unleashed its fury upon the innocent people of Atlantis. Determined to distinguish himself from his father's legacy, Mark surged back with renewed vigor to aid in the defense. Despite his valiant efforts, he was still dragged into the depths, only narrowly escaping to the surface, unnoticed. Cecil counted his blessings that Mark had survived. Meanwhile, Donald remained oblivious to his cloned existence.
Eve's father offered a contrasting perspective on her work in Chicago, revealing that the areas she had reconstructed had crumbled into unstable ground, areas the city had previously deemed unsafe and fenced off. Debbie, confronted with the metaphor of a broken cabinet door, tore it from the wall in frustration, her pain unsoothed even by Mark's comforting words. Shapesmith unveiled his false origin story, accompanied by imagery of sequids fleeing a doomed Mars. The Supreme Lizard met his demise at the hands of a loyal follower to King Lizard.
In the epilogue, Angstrom abandoned a captive, malevolent Mark to the mercy of female counterparts of Cecil and Donald, leaving his fate hanging in the balance.
