You need to take out the blimps in the sky, since they can monitor your movements and conversations. Head to the first marker and use Galleth to get to the top. Note that when you grab onto the hook, you'll need to hold R2 down before you can press X to jump. At the top, use the last hook to disable the first balloon.
Head to the second tower. This time, you'll need to properly time your jumps off the hooks so you can latch onto the next one. As you climb up, you'll undoubtedly see a Secret Sly Mask hidden behind some breakable objects. Wait until you disable the balloon, then drop down and grab it.
The third, and last, tower isn't that much harder. There will be spire jump points rotating, meaning you will need to time your jump off the hook so you can land on one of these spires. After, you will need to get to the other side of the tower, where you will repeat this. Do this again to reach the top and disable the last balloon to finish the mission.
