Free the Red Sage was a mission that Jak and Daxter completed to obtain a power cell in The Precursor Legacy. One of four sages that was kidnapped by Gol and Maia and brought to their citadel until Jak freed him from their captivity in this mission.
The PlayStation 3 and Vita versions of this mission are related to a trophy named "Set Me Free!", completing this mission will reward you with a bronze trophy.
The first obstacle you come to is a number of half and quarter-sized modified precursor platforms that lead into a large bottomless corridor. At the end you'll encounter a large colored platform bridge (activated by a button) which winds around a corner. Stepping on a platform causes all platforms of that colour to drop, so it's recommended to long jump to the left as far as possible to avoid de-activating too many platforms and then making your way to safe ground.
Having advanced from this area, you come to a thin and long hallway with a large machine at the end. Play pauses and Daxter's words warn of a huge swarm of approaching citadel bunnies. There are two eco vents in this hallway to aid your success; one yellow and one red. First you will need to use yellow eco to break through the lurkers in the hallway to reach the red eco. From here you can destroy the three generators at the end of the room with ease to shut down the machines spawning lurkers.
Once you've destroyed all the lurkers a door will open leading to another bottomless corridor with more of the spinning, fragmented, circular platforms that appear all over the citadel. Once you have passed this area, smash the generator to free the Red Sage and collect a power cell.