After meeting with the Templar, leave the inn and head to Church's place together with Lee. As you get there, it will turn out that the man has been kidnapped.
To find him, you need to eavesdrop on the neighbours of the abducted, marked on the map. For that, enter the circle displayed around them.
As you're eavesdropping, you cannot be noticed by civilians, so hide between the men leaning against the wall on the right.
After they stop talking, you will receive a mission of climbing onto the top of the nearby church.
Climb to the top and press the interaction button. That way you will synchronize and discover a big part of the map. There are many such points in the game, marked with an eagle icon on the map.
Optional objective: Eavesdrop on a moving group of guards.
Optional objective: Do not fail a single eavesdrop.
Optional objective: Completed all the constraints in one playthrough.
With the synchronization complete, jump onto the haystack (press the free run and jump button at the same time). You will receive two additional objectives: you need to eavesdrop on the moving groups of guards and not fail any chance.
First four groups will be marked with orange dots, but after eavesdropping on one of them the others will disappear.
Your main target should be the soldiers left of the church, as only they are moving. That way you will complete the first additional objective.
After the first eavesdrop, head to the green circle marked on the map. Search the designated area and you will find another group of soldiers. Approach them and sit on the nearby bench to mix into the crowd.
Further people to eavesdrop on can be found in the second green area. After listening to the whole conversation, you will complete the additional objective.
Not together with Lee you have to sneak to the marked red zone. Within it, guards are very suspicious and will start chasing you on sight, so be very careful. You can give your companion some easy order with the interaction button, telling him either to follow you or stay where he is.
You can also point to a hiding place (aim button) and tell Lee to hide there (interaction button).
In order to reach the suburb warehouse unnoticed, go round the red zone from the north.
Optional objective: Remain undetected.
You will come across only one patrol there. Hide in the bushes and head to the door after they disappear. Unfortunately it will turn out to be locked.
The key is in possession of three guards in the area. The easiest to steal from is the one on the right. Firstly lure the man walking around the warehouse and kill him with the hidden blade. Afterwards sneak to the target and hold down the interaction button to get the item.
In order to complete the additional objective, you have to remain undetected.
Having obtained the key, enter the marked warehouse where you will find three men torturing Church.
Kill the two closest enemies together with Lee and afterwards get rid of the third one to finish this chapter.