This is the first templar hunt quest for Rhona Dinsmore, the primary Assassin contact in Havana. To start it, talk to Rhona, who can be found in the southern part of Havana.
Edward finds Master Assassin, Rhona Dinsmore, in the middle of combat and decides to help.
Start by taking out the two soldiers who will run in from the north and attack you.
There are three possible entrances in the courtyard from which soldiers will run in. You will have a little over 40 seconds to prepare for battle, and you will need to defeat three waves of soldiers in total. If you need extra health or bullets, you will find some in the courtyard.
Follow Rhona's instructions - pick up the small explosive barrels scattered around the courtyard...
...and place them near the entrances or wherever you see fit. Rhona should also place a barrel by one of the entrances.
When the timer runs out, guards will appear and try to run up and attack you. Use your pistols to shoot the barrels when enemies are nearby to blow them up. You certainly won't be able to kill everyone this way, so take down any survivors who break through in sword combat.
Once you kill all the attackers, the preparation phase will start again. With each wave, there will be more soldiers, and in the last one, a Brute will also appear.
After getting rid of all three waves of enemies, the quest will end, and after a cutscene, the next quest in this chain will be unlocked. - A Thief in the Market.