Rescue the girl! is the second mission of Size Matters. Ratchet and Clank went after the robots that captured Luna before it was too late. After fighting through several robots, they almost managed to rescue her, however, the robots escaped to Kalidon on their ship. As the robots stowed Luna aboard the ship, one of them dropped a small item, which, through close observation, Clank believed to be a technomite artifact, but Ratchet was convinced technomites are make-believe. Clank disagreed and also pointed out that this device was why the robots captured Luna.
Qwark then managed to catch up to them and upon seeing the artifact, excitedly grasped it from Clank's hands and was amazed by it, as he shared how he heard about the technomites, much to Ratchet's annoyance. Clank reasoned with him that this artifact was their only lead to rescuing Luna, as it contained coordinates etched on the side. Ratchet sourly agreed and swiped the artifact from Qwark, telling him to stay out of their way.
Now your new objective is to find and rescue Luna from the robots. Walk on past the house the robots blew up and prepare to fend off more scuttle crabs and several guard torsos. You will eventually come across a black metallic wall that you can walk on, using your Gravity Boots. Upon reaching the top section, lay your attacks on the robots ahead. Head forward and to your right is a zipline that will lead you down to the lower platform, where you will encounter more enemies. Destroy them and then proceed on into the small cave, where you will find several crabs and some robots. Upon exiting the cave, lay the smackdown the four crabs the appear from the water. This area marks another checkpoint.
Hop onto the raft that will take you to the island ahead. Watch out for the robots that will confront you along the way. This maze-like island will be swarming with crabs, so keep your eyes and ears open. Head forward to find another raft that will continuously lead you through the waters until it reaches a dock. Along the way, shoot down any robots that attack, and also note that there are a few islands with bolt crates you can smash. You can hop to them as long as you're close enough to them. Upon reaching the dock, make your way through this lounging area and defeat the last group of enemies. Finally, to the left is an elevator that you must take to complete the mission.