This quest can be activated if you complete the quest Get permission from Metzger for gang war.
Go to the church where Tyler's gang is guarding the chemicals. Ask about what's going on: you will need a Charisma of 5 or more in order to progress the quest (having less than 5 only lets you give Tyler a casual greeting without consequences, keep talking to him and eventually he will tell you of the party, and you can progress.). Tyler will reveal that they are throwing a party.
When you return to Lara, you will find that you cannot collect your reward from her. Instead, she will demand that you help her attack the gang.
- 200 XP