Doc, Drew and Zak Saturday are on their way to Manaus, Brazil on their airship, where they have hidden their piece of the Kur Stone. However, V.V. Argost already knows where it is and is already on his way there. Drew explains that one of the most dangerous cryptids known as the Tapire-Lauara lives there and is the reason they chose that spot to hide the stone fragment. If they are unable to stop Argost before he gets there, Doc tells Zak they may need his powers to control the Tapire-Lauara long enough for them to retrieve the stone piece.
In order to help Zak control his powers, Doc gives him an artifact he invented that he can use to attach the Hand of Sul-Kalu to. After sparring with Doc, Zak is able to try it out and get used to it. He ends up calling it "The Claw." Meanwhile, Drew tells them that they've finally found Argost's ship, which has begun to attack them. Drew tries to maneuver the airship to avoid his attacks, but it's no use.
Since his parents are having a hard time trying to avoid Argost's attacks, Zak comes up with an idea and takes Fiskerton with him outside to one of the wings on the airship. He plans to have Fiskerton throw him towards Argost's airplane and take care of Argost himself. However, Drew sees him on one of the monitors and maneuvers the airship so that Zak and Fiskerton are back inside. In doing so, their airship is shot down and crashes in the rain forest below.
As they reunite with each other on the ground outside, Drew is angry at Zak for trying to do such dangerous stunt, while Zak is angry with her for not giving him a chance to prove himself. Doc decides to talk to him one-on-one and explains to him why he has his cryptid-influencing powers. Since Drew believes in the theory that for every action, there's an equal and opposite reaction. He and Drew brought the potential for evil into the world 11 years ago, which was the same year Zak was born.
Doc tells Zak that if Argost is able to summon Kur, he'll have the power to raise an entire army of cryptids, which only Zak's power will be able to stop. That is why he and Drew are afraid that if the Kur is unleashed, Zak may their only hope. After their conversation, Drew calls for them, as she, Fiskerton and Komodo are being attacked by a pterodactyl-like cryptid. Doc tells Zak to use his new invention to try and stop it. However, his powers don't have any effect on it and is taken hostage by the cryptid.
Drew is able to shoot it down with her sword before it gets too far, making Zak fall back to the ground below. Before she can go check on Zak, the cryptid returns and begins to attack her and the others. While they are pre-occupied with fighting it, they are all tied up against the trees by the rain forest vines. As the cryptid is about to eat them, Zak returns and is able to use his powers to calm it down and is able to untie them all. Doc tries to analyze the cryptid, but can't find any information on it. Zak explains that the reason it started attacking them was because they crashed through her nest with their airship.
Meanwhile, Argost's plane flies overhead, so the Saturdays walk towards the spot where the stone piece is hidden. Luckily, there are no Tapire-Lauara in the area, so they are able to dig up the stone piece without any trouble. However, Argost's plane had been following them and arrives at their location. Doc tells Drew to run off with the stone piece while he and Zak deal with Argost. But before she can get away, Argost descends from his plane and unleashes several Devonian Annelids on them, which drain them of their energy, causing them to lose consciousness.
When they awake, the Saturdays find themselves tied up and unable to break free. Before Argost leaves with the final stone piece, he wants to see them all get eaten by the Tapire-Lauara and orders the cryptids to eat them. As the Tapire-Lauara approach, Zak tries to use his power to control them. They appear to be too strong for him at first, but he is able get them to stop from a brief moment until Argost orders them to attack once again. Using his powers, Zak is able to use one of the Tapire-Lauara to break free so he can reach the Hand of Sul-Kalu.
Before Zak can free his parents, Argost tells Munya to stop him. Zak distracts him by throwing mud in his face and goes after Argost before he can escape. He uses the Hand of Sul-Kalu to knock the stone piece out of his hands, making it fall on the ground. Zak uses his powers so that the Tapire-Lauara can attack Munya while he gets the stone piece. However, Argost tries to stop him by throwing Mongolian Deathworm Venom bombs at him, but he misses. Zak catches one with the Hand of Sul-Kalu and throws it at the vines tying up Fiskerton, partially freeing him.
Argost tries to fight Zak directly using Drew's sword, while the others try fighting off the Tapire-Lauara. As the battle continues, Doc is able to get himself free and Zak is able to gain possession of the stone piece. Meanwhile, the pterodactyl-like cryptid from before returns to help them by attacking Argost. But he is able to hold it off long enough to try and throw a Mongolian Deathworm Venom bomb in its mouth to melt its insides. Zak sees him and tries to help, but Munya uses the opportunity to take the stone piece from him, leaving Zak with the decision to either help the cryptid Argost is about to kill or chase after Munya and retrieve the stone piece. He decides to do the former and helps the cryptid get away, but in doing so, he allows Argost and Munya to make their escape with the final Kur Stone piece.
Zak apologizes for letting them get away with the stone piece, but Doc tells him he made the right decision in a tough situation. Drew also points out that the stone piece left an imprint in the ground when it fell during the battle earlier, which they can use to try and figure out Argost's next move. The cryptid Zak helped save also returns and he names it Zon. They bring it back to the Saturday headquarters to live with them. In the lab, Doc and Drew attempt to decipher the Sumerian language that was left by the stone piece imprint. Meanwhile, in his lair, V.V. Argost begins the broadcast of his show, Weird World. He tells his viewers that he's recently come into possession of the key to unlocking the greatest secret in history and can't wait to show the whole world what he finds.