The game's plot opens with the anthromorphic character Ratchet meeting the robot Clank on his home planet. Clank discovers that the villainous Chairman Drek of the Blarg race plans to create a new planet for his species, destroying the galaxy in the process. Clank convinces Ratchet to help him in his quest to gain the help of the famous superhero Captain Qwark, but they soon discover that they must save the galaxy on their own.
The game offers a wide range of weapons and gadgets that the player must use to defeat numerous enemies and solve puzzles on a variety of different planets in the fictional "Solana" galaxy. The game also includes several mini-games, such as racing or lock-picking, which the player must complete to proceed. The game was positively received by critics, praising the good graphics and variety of gameplay along with the sci-fi story.
In Ratchet & Clank, the main playable character is Ratchet, whom the player controls from a third-person perspective. The player traverses diverse environments with a large collection of unusual gadgets and weapons, using them to defeat enemies and pass obstacles. Up to 35 weapons and gadgets can be bought or found in the game. The player begins the game with only two weapons; the "OmniWrench 8000", a standard melee weapon with a variety of uses, and the Bomb Glove, a short-range grenade thrower. As missions are completed across the game's various planets, more weapons and gadgets become available, including the Blaster (automatic pistol), the Pyrociter (a flame-thrower), and the Suck Cannon (a weapon which sucks up smaller enemies and converts them into projectiles). Weapons are either found, or can be bought with bolts, the game's form of currency.These bolts can be found in crates, along with ammo, or dropped from defeated enemies. The player also needs to buy ammo for most weapons, but a small number can function without the need for ammo. Vendors, which sell weapons and ammo, are situated at strategic points throughout levels. After completing the game, the player may choose to enter "challenge mode", in which the game's difficulty level rises considerably, but all bolts and weapons acquired the first time are carried through. There is also the option to buy "gold weapons", more powerful versions of existing weapons. The game's health system, nanotech, starts at four health bubbles, but upgrades can be purchased, giving the player a total of eight hit points.
Normally, Clank rides on Ratchet's back, acting as a jet-pack or similar device. Occasionally, however, Clank becomes a playable character when Ratchet is unable to explore certain areas. Clank can control "Gadgebots", smaller robots similar to Clank, who perform certain actions for him. Racing, in the form of hoverboard races, appears in the game. Some racing missions are necessary to progress in the game, while others are optional. One level of space combat and a level of flying through the air shooting tankers is also present. Mini-games to unlock doors, extend bridges, or elevate platforms appear in most levels.
On planet Quartu, an assembly line is producing large, destructive robots when suddenly there is an error, and a small, curious robot emerges. The robot encounters a video recording on an infobot. Horrified by its contents, the robot escapes the planet in a spaceship, only to be shot down over the planet Veldin.
On Veldin, a lombax named Ratchet is constructing his spaceship when the robot crash-lands near his home. Ratchet recovers the robot from the wreckage, nicknaming him "Clank". Clank shows Ratchet the infobot, which contains a recording of Chairman Drek of the Blarg race, who explains that his home planet is uninhabitable due to pollution and overpopulation. Drek's solution is to build a new planet for his race by extracting large parts of other planets, destroying them in the process. Fearing that Drek will destroy the galaxy, Clank asks Ratchet to help him find the famous superhero Captain Qwark, in an effort to stop Drek. Ratchet is eager to leave Veldin in his ship, but can't without a vital component: a robotic ignition system. Equipped with a robotic ignition system, Clank starts Ratchet's ship in return for his help.
The two later find Qwark on planet Rilgar. Qwark encourages them to prove their heroic status by completing a dangerous obstacle course on the planet Umbris. After they finish the course, however, Clank leads himself and Ratchet into a trap laid by Qwark, sending the two into a cavern. Here, Qwark reveals that he is working for Drek in order to become the spokesperson for the new Blargian planet. Qwark leaves the two to fight a monstrous Snagglebeast.
After defeating the Snagglebeast, Ratchet becomes increasingly bitter and hostile towards Clank, angry that he let Qwark get the better of them. Clank urges Ratchet to continue their quest to confront Drek, but Ratchet is obsessed with getting revenge on Qwark. Eventually, Ratchet carries out his revenge on Qwark in a space battle. Afterwards, Drek attacks a nearby planet. Witnessing the devastation Drek causes, Ratchet finally understands that he must be stopped and makes amends with Clank, admitting his selfishness in focusing on Qwark.
Combining their efforts, Ratchet and Clank learn that Drek has developed a weapon called the "Deplanetizer". Drek aims to use it to remove Veldin, Ratchet's home planet, from the desired orbit of his newly constructed planet; and this enrages Ratchet. On Veldin, Ratchet and Clank confront Drek, who is about to obliterate the planet. Drek reveals that it was he who polluted the Blargian home planet in the first place, and he plans to do the same to, and make more money from, his new planet after the living space has been purchased.A battle ensues, after which Drek is killed. Ratchet uses the Deplanetizer to destroy Drek's planet, sending meteorites falling towards Veldin. A meteor impact throws both Ratchet and Clank off of the platform; Clank manages to grab onto the ledge and catch Ratchet, but the strain of supporting Ratchet's weight causes heavy damage to Clank's arm. Ratchet offers to repair Clank, and as the game ends they walk off together as a team.