Cole would approach a concerned civilian, who would inform him of the courier's presence within the area. The courier would deliver a package of five blast shards to a certain location. Cole would have to stay out of sight and tail the Reaper until he reached his destination, after which Cole could retrieve the shards.
Instead of a combat mission, this is purely a stealth scenario. If the courier spots you, he will attack you and detonate his explosives rigged onto him, just like the Reaper bombers. While following him, you may not kill him until after he drops off the package.