You must be Level 10 and above to do the party quest.
For a complete video guide of this PQ, click the Play button above (thanks to AionJC).
Either head to Henesys Park or enter the map [node:13639 link] through the Dimensional Portal (shown above) and form a party of 3 or greater up to a maximum of 6 people. The recommended levels for this quest are 10-20.
Your party leader must talk to the NPC Tory to begin the party quest. You will have 10 minutes to complete the party quest.
(This PQ is previously known as the Henesys Party Quest.)