Tiff ( -231, -46, -847 ) /waypoint -231, -46, -847 gives you a courier costume to wear and sends you to Blackshield dock area.
The courier costume is a NO-ZONE fashion outfit (worn in the chest slot like all fashion outfits). Must be EQUIPPED, not just appearance slot.
Approach the two Blackshield NPCs in the Blackshield area overlooking the docks ( -468, -92, -963 ) /waypoint -468, -92, -963 while wearing the costume. They will talk (while you eavesdrop) and then, thinking you're the courier, hand you a magically sealed document.
Take the document back to Tiff who will then tell you to deliver it to the intended recipient at Pride Lake.
Meet the mysterious contact, a dark elf, on the southeastern bank of the river right where it flows out of Pride Lake ( 437, -45, -368 ) /waypoint 437, -45, -368 while wearing the costume.
Return to Tiff so that she knows the contact has the scroll.