S1 M3: A Journal - Assassin's Creed Revelations
After killing the four guards walk over and talk to the treasure hunter, who tells you about the keyholes in the door -- sending you in search of the book in the library that answers the question of the locks on this door.
The Full Synchronization for this Memory is "Do not fail a single tail" -- gah!
Following Undercover for Full Synchronization
Our first task is to find the Templar Captain and retrieve the journal -- so walk up the hall and through the door, and to the outer door where we are treated to a CS of the Captain departing, instructing the guard that the Assassin must not get his hands on the book -- yeah, the book...
Basically you have to work your way through the town, tailing the group fairly closely to find the Captain. As near as I can tell if you mess this up you cannot restart the memory -- which means waiting for a group of guards to kill you (which can take bloody for ever) is the only way to reset it without having to replay everything... If you make any overt acts around the pilgrims on the road they go aggro on you for some reason, which then blows your cover with the Templar, so do not do that.
Giving them the Tail
Getting 100% synchronization on this memory seems to be universally annoying for most gamers -- so do not feel bad if you end up having to try to get it several times -- it is one of the more tedious synchronizations in the game it seems.
Once you follow them to the bottom of the town you start the next memory.