This game takes place after the events in Ape Escape, where Kakeru (Spike in the U.S. version, named "Spike" in the original U.K. Ape Escape) stopped Specter from taking over the world. It is a few years later, and The Professor left for a vacation leaving his granddaughter, Natsumi (Natalie in the U.S. version), and Spike's cousin, Hikaru (Jimmy in the U.S. version), to watch over the laboratory. The Professor has left them with one task: deliver a load of monkey pants to the monkeys in Monkey Park. Hikaru accidentally sends not only the monkey pants, but The Peak Point Helmets as well. Specter gets a hold of one, and yet again makes an army of monkeys bent on ruling the world. Jimmy aims to capture all the monkeys and stop Specter. However, Specter has supplied five monkeys with Vita-Z bananas, making them stronger and more intelligent than the average monkeys.
Hikaru manages to capture all of the Freaky Monkey Five, except Yellow Monkey. Before his fight with White Monkey, Pipotchi, a baby monkey accompanying Hikaru, is kidnapped, in order to transfer the data in his Peak Point Helmet into a device called the Lethargy Laser. Rescuing Pipotchi, Hikaru makes his way through a monkey controlled military base, and confronts Specter, who is waiting for him with a hi-tech gunship. Before the two can battle, Yellow Monkey, now a giant monster thanks to an overdose on Vita-Z bananas attacks the facility. Specter flees, and Hikaru manages to downsize and capture Yellow.
Hikaru, the Professor and Natsumi then discover the purpose of the Lethargy Laser. By firing it at the globe, all humans worldwide will lose the will to fight back, making it easier for Specter and the monkeys to take over the world. Hikaru confronts Specter at his moonbase, who attacks him with a giant robot. Once defeated, Specter attempts to fire the laser, but Hikaru states that humans will never give up, and captures him. Jimmy and Pipotchi then flee the exploding moonbase.
Shortly afterwards, Specter escapes and goes into hiding. Hikaru then proceeds to capture all the remaining monkeys before the Professor discovers Specter's hiding place. Hikaru warps there, encountering Specter, and the two of them battle again. Specter loses and is once again captured. The game ends with Spike visiting the laboratory, which is destroyed when Hikaru accidentally crashes a spaceship into it.
Gameplay is similar to the previous game. Movement is controlled with the left analogue stick and R buttons, and gadgets are controlled with the right analogue stick. Three new gadgets are added, the Electro Magnet, used for pulling metal blocks and clinging onto metal surfaces, the Water Cannon used for putting out fires, and the Bananarang, that can attract monkeys with a banana fragrance. A new feature is the ability to change the gadget loadout by holding down one of the gadget buttons and changing the gadget.
Also introduced in this game is Pipotchi, a sidekick who can assist Jimmy in reaching ledges and occasionally revive him if he's knocked out. Also, the gotcha coins that spawn from enemies are used as currency for bonuses, and can multiply in worth if left alone.
Source: Wikipedia, "Ape Escape 2", available under the CC-BY-SA License.