This missions appears later in the game. The suggested level is 250.
The beginning of this mission starts when Hytham request to see you in camp at his house. Then see Ranvdi and ask to see the Alliance map. Wincestere is in the center of Hamtunscire, which is located in south west of the England map.
The arc itself is straight forward, and deals with taking out members of the Order of the Ancients. Only 3-4 mini missions.