Full Synchronisation Requirement - Kill 5 Templar guards from a haystack.
After the cutscene, Leandros will send three of his Templar henchmen to take you down. This is an excellent opportunity to pick up a the "Silent but Deadly" Trophy/Achievement. If you want to try and get it, equip your throwing knives and press and hold the throw button to charge up, releasing three knives at once and killing all three Templars. If not, just take them down as you’ve been doing so far - try and counter kill one then combo the other two with executions!
Loot the bodies to find replacement knives and poison (if you’ve used any so far!) as well as bomb ingredients to be used later in the game. Follow the path towards the water wheel, either avoiding or quietly assassinating the patrolling Templar on the walkway. Once you’ve reached the marker, Ezio will climb onto the wheel ride it to the top of the wall. Assassinate the Templar and follow the stairs down and around. Wait until the Templar near the haystack has moved away from it before climbing into it. When he approached, hold in the 'High Profile' button and wait for the prompt to assassinate him to appear onscreen. Do so, and instead of hiding the body in the haystack, toss it into the open area, in view of the other two patrolling guards who will soon pass by. Hide in the haystack again, and when you see your chance, assassinate another one from the haystack as they examine the body. It doesn’t matter if you get detected by the remaining Templar, just take him out quickly. Be careful though, as until you find medicine your health is low and escaping is very difficult as your acrobatic abilities are diminished by your injury. Follow the path around, avoiding the pair of guards further along.
Once you reach the market-like area, move from crowd to crowd, using Eagle Vision to track the trail of Leandros. When you reach another haystack, hide in it and wait for the patrolling Templar to pass by. This time, don’t use the 'High Profile' assassinate, just wait for him to stand almost on top of you and assassinate him, pulling him into the haystack for a stealthy kill. Continue up the hill moving from group to group and try and avoid confrontation with the patrolling guards. When you reach the gatehouse, Leandros will taunt you and send more Templars after you.
Carefully time your presses to counter their attacks and kill them, before looting the bodies for medicine and more bomb materials. Hug the wall to the right and move around the buildings, and you’ll see a lone Templar standing next to a third haystack. Jump in it and take him out before heading to the rooftops. Try and avoid being detected by the riflemen on the rooftops, and if any of them catch a glimpse of you, you can quickly rush them and assassinate them before they raise the alarm. From the rooftops you should be able to see a line of Templar guards blocking the road. Leap into the left haystack from the roof, and then instead of moving to the objective marker at the foot of the tower, instead head to the other haystack. Climb up the wall a little and wait until you have the attention of one of the conversing guards who should come to investigate when the meter begins to flash red. Jump down and hide in the haystack again, and wait for him to come near. As you’ve already been doing, assassinate him from within the haystack for your fifth and final kill needed for 100% Synch. Now it’s time to finish off Leandros, so begin to climb the tower. The Templar riflemen will automatically spot you and start shooting, but fortunately for you they’re not the most accurate of shots. Make your way up the wall, stopping to avoid being hit by the body of a falling Templar thrown by Leandros. When you reach the rope, jump to it and you’ll be pulled to the top of the tower, ready to confront him finally. When the fight begins, simply counter one of his attacks to bring him down.