You need to go to Arsuf, which is near Acre (you can teleport there from menu).
Kill three archers on your way.
Under the palisade provoke soldiers to come to the other side. Kill them while riding a horse.
You will be attacked by group of soldiers so use counterattacks carefully.
Clear your way to the next palisade.
After the talk you will need to fight a very strong group of knights. Use counterattacks.
The last one is Robert de Sable. His blows take two blocks of energy so be careful.