This is a discussion on Chapter 5 help within the Rocketbirds: Hardboiled Chicken forum, part of the R; im stuck at the start i just killed everybody with the brainbug or whatever and i have the blue keycard ...
Sorry for taking so long to reply to your question. I never noticed this thread until someone else pointed it out to me. I checked your trophies and seen you already have the plat but I'll answer it anyways for other people who may be stuck at chapter five as well.
After you get the blue key card, you need to go all the way to the left of the level and take the elevator down. Next, use the box to jump up to the ledge and open the door with the blue card key and continue right and I believe in the next screen there is another elevator. Take it down and then head to your left and release all four prisoners. After doing so, head to your right and drop down into the room and kill all of the penguin guards while making your way to the right. Eventually you'll have to climb up and go right. This will take you to a room which got writing on the wall saying:
"Four Legs Good, Two Legs Better or Badass" I can't remember for sure.
Anyways, in this room there will be two penguins below. One of them will pace back and forth. Once he steps on the elevator, press the button to bring him to the upper level. Next throw a Brainbug through the vent to get control of him and open the door. Then you can drop down to the lower level, get your gun back and the green key card and make you way back to the spot where a penguin is going back and forth on the moving platform. Kill him and jump on and make your way back to the where you used the blue key card. From here, ride the elevator back up, bringing the box with you and then jump up and continue right until you arrive back at the locked up Cardinal prisoner. Once you open the door, he'll provide an exit for you and you can pass the chapter.