Go to Qufim Island and inspect the Giant Footprint at (E-6) - located in the tunnel that leads to Behemoth's Dominion - for a cutscene and to spawn your NPC buddy and the NM Gigas named Ingaevon (level 53-55).
If it says, "There is a gigantic footprint here," you'll have to wait a short time (~5 minutes) to start your CS.
Once you have defeated the NM, speak with your NPC before doing anything else or you can glitch this level cap quest in a way GMs are not able to reset! It's not necessary to click on the Footprint again.
If you have failed to talk to your NPC and they disappear, zone into Behemoth's Dominion, just down the hall. Zone back in and you should be able to fight the NM again.
Speak with Luto Mewrilah for a cutscene regarding the truth about Pembroke.