A gigantic seaquake opens a time warp that admits aquatic dinosaurs from the ancient past, as well as Niccol and other criminals from the year 2098, into Aquaman’s present. The seaquake is even felt in Mera’s fourth-dimensional world, and she comes to Earth to investigate. The criminals take control of Mera and the dinosaurs with a thought-control ray from their era and briefly turn them all against Aquaman and Aqualad, until the two heroes seize the weapon and free them from the villains’ domination. The dinosaurs and criminals are restored to their proper eras, and Aquaman destroys the futuristic weapons.
A powerful earthquake, deep beneath the waves, generates a tremendous tidal wave that threatens to capsize an oil tanker. Arriving on the scene, Aquaman summons several pods of whales to serve as a barrier between the wave & the tanker. Investigating the epicenter of the seaquake, Aquaman and Aqualad discover a rift in time and space, revealing multiple rifts along the temporal continuum. The rift manifests as a series of corridors leading to different eras, the opening of one corridor exiting into present day. The two heroes witness a Hesperornis and a Meganeuron, a prehistoric water fowl and dragonfly, respectively, enter their time through the portal. Fearing something worse will soon make it's way into the present, Aquaman summons a pod of whales, along with several squid, to ram a sunken German U-Boat into the portal, sealing it. However, upon reaching the surface, Aquaman and Aqualad see the U-boat violently break the ocean's surface, as if hurled by a great force. Behind the submarine, another prehistoric creature, this one a Plesiosaur, emerges from beneath the waves. The Plesiosaur moves in to devour Aquaman's finny friends, prompting Aquaman to instruct the pod of whales to forcibly launch him into the air, via water expulsion from their blowholes. Aquaman barrels into the Plesiosaur, then dives beneath it, luring it away from the endangered fish. Swimming all out, Aquaman leads the Plesiosaur back down to the temporal portal. Before he can reach it, though, a Tylosaurus emerges into the present, blocking the portal entrance as it charges towards Aquaman. Caught between the two prehistoric reptiles, Aquaman suffers a blow to the head from the Plesiosaur's enormous fin and falls into unconsciousness. Aqualad races to get his mentor clear of the dinosaurs, but while carrying Aquaman, he is too slow to outpace the prehistoric creatures. As they close in on the aquatic aces, Aqualad turns to face them, preparing to lay down his life for Aquaman.
The creatures are seconds away from devouring Aqualad. Suddenly, they are enveloped in hard water cages, that then carry the dinosaurs to the surface. Mera has arrived, in the veritable nick of time. The seaquake was so severe that her realm in Dimension Aqua also felt it's effects. Mera decided to investigate the disturbance, happening upon Aqualad's dilemma. Ascertaining that Aquaman's injuries are severe, Mera rushes him to the Aquacave. There, Mera brews a kind of tonic, from seaweed, that instantly revives Aquaman. Feeling renewed vigor, and heartened by Mera's presence, Aquaman leads Aqualad and Mera back to the surface, to resolve the situation with the dinosaurs. There they find that the creatures have escaped Mera's bonds, and are menacing passing ships. The Plesiosaur upends one such vessel, dumping it's crew into the ocean. Then, to the amazement of the three heroes, the Plesiosaur steals the ship, racing away at high speed with it's prize. Mera uses her power to control water to build a bridge to the mainland, allowing the capsized crew to make their way back home. Aquaman, Aqualad, and Mera trail the Plesiosaur to a small island. The Plesiosaur seems to be following the commands of a strange trio of men. Summoning a group of giant tortoises, Aquaman steals onto the island, using the oceanic reptiles for cover. Eavesdropping on the men's conversation, Aquaman learns that they are criminals from the year 2098. They escaped the authorities of their time through one of the temporal rifts. In their possession is a weapon that allows them to control the thoughts of other creatures, be they man or beast. The men plan to return to their time to steal more of the thought controlling weapons, then seal the portal with another weapon called a "Z-Gun", thus eluding the police from their era forever. Flanking the future crooks, Aquaman and Aqualad mount a frontal assault, while Mera engages from the rear. The leader of the future fugitives, a man called Nicoll, spies Mera racing up behind them, protected by a hard water shield. He instructs his men to open fire on her with the Z-Gun, which shatters her hard water barrier. Nicoll then aims the thought control device at Mera, turning her against Aquaman and Aqualad.
Diving back into the ocean, Aquaman and Aqualad flee the more powerful Mera. Mera constructs an enormous, hard water, toothed shell, that she sends in pursuit of the aquatic aces. Unable to keep up with his much faster mentor, Aqualad is soon engulfed by Mera's shell. Aquaman continues to swim an evasive pattern, racing back to Mera's still standing, hard water bridge. The shell crashes into the bridge, breaking apart and freeing Aqualad. Aquaman and Aqualad attempt to dive beneath the waves, but Mera lashes a hard water rope around them, stalling their escape. Aquaman summons a whale, ordering it to batter Mera with it's tail. With her concentration broken, the hard water rope dissolves back into ordinary seawater. Aquaman and Aqualad quickly make for a series of coral caves, the labyrinthian structure of which provides the perfect hiding place from Mera. Meanwhile, Nicoll has returned to 2098, to retrieve more thought control devices. Knowing that time is running out, Aquaman enacts a desperate plan. Riding atop what appears to be a low laying black cloud, Aquaman herds the Plesiosaur and the Tylosaurus back towards the island. Turning the thought control device on Aquaman, the future felons order Aquaman to turn back, but the dinosaurs continue closing on the island. Switching to the Z-Gun, the fugitives from the future, take aim on Aquaman. Mera, no longer under the influence of the thought control weapon, sends a massive hard water fist crashing down on the two crooks. Before they can recover, Aquaman and Aqualad disarm them. Aquaman uses the thought control device on the two criminals, ordering them to return to their era and surrender to the authorities. Aquaman then explains that the "cloud" he rode in on is actually a small ice berg, painted black by squid ink. Since the dinosaurs come from a more tropical era, Aquaman surmised that they might not cotton to cold water, and would, in fact, swim towards more temperate waters. A pod of whales were instructed to push the iceberg, running the dinosaurs aground on the island. Aquaman uses the ice berg to drive the dinosaurs back through the portal, then destroys it with the Z-Gun. Upon breaking the thought control device, too, Mera teases that she would have liked to use it on Aquaman, to get him to like her. Aquaman confesses that he already does.