Ratchet & Clank: Size Matters is a platform game in the Ratchet & Clank series for both the PlayStation 2 and PlayStation Portable. It is the first Ratchet & Clank game on the PSP handheld, and the fifth, chronologically, in the series. It was developed by High Impact Games, a company spawning from the original Ratchet & Clank developer, Insomniac Games. The story is about Ratchet and Clank as they are interrupted from their vacation to search for a kidnapped girl and encounter a forgotten race known as the Technomites.
While on a vacation on Pokitaru, Ratchet and Clank meet a little girl named Luna who is writing a school report on heroes. Shortly after they meet her, Luna is kidnapped by mysterious robots. Clank then stumbles upon a mysterious artifact from an ancient race, the Technomites. Although Ratchet is initially skeptical about their existence, Clank believes they do exist. Ratchet and Clank set out to save Luna and in the process, encounter Captain Qwark, who is attempting to find his birth parents. Ratchet allows him to use his ship's computer to aid in his search, in order to make him stop following them.
On Kalidon, Ratchet is kidnapped by Luna, and Clank is left in a junkyard on Metalis, however Clank turns into a bigger Clank and sets off to destroy enemies and to save Ratchet. Meanwhile, Ratchet's DNA was taken in order to produce an army of clones. Emperor Otto Destruct, leader of the Technomites, has recognized Ratchet's potential and hopes to use his DNA to produce the ultimate soldier. After being tracked down and defeated on Dayni Moon, Luna reveals the clone plot to Ratchet and Clank and explains the Technomites are bitter for never receiving credit from the general population for their technological advances.
After defeating Luna, Clank tries to get the clone factory co-ordinates from Luna, but is infected with a computer virus and malfunctions, allowing the Technomite soldiers inside Luna to enter Clank. Ratchet uses his shrink ray to go inside Clank, meeting his internal security system, and they collaborate to eliminate the intruders and restart Clank's processor. Clank reveals that he did obtain the factory co-ordinates before being deactivated, and they head to a planet known as Quodrona. After Ratchet kills dozens of clones, Otto reveals that what Luna told them was a "(cheesy story)", and his real plan is to steal the intelligence of every being in the galaxy, using a special machine that transfers the intelligences from one being to another.
Qwark, persuaded by Otto, thinks Otto is his father and temporarily fights on his side. Ratchet and Clank eventually defeat him after a long and hard battle. After beating Otto, they learn from Skrunch that Qwark's real parents were killed by defective equipment made by the Technomites. Qwark tries to use Otto's machine to give Otto the intelligence of himself, Skrunch interferes and Otto then gains the intelligence of Skrunch. Back in Ratchet and Clank's apartment, shrunken Ratchet clones are sold like toys and keep the shrunken Qwark company, while the two heroes watch TV.