Petty's Patties Trophy
Complete Mission 4: Petty's Patties
Story related, cannot be missed. You'll obtain this trophy after completing Mission 4: Petty's Patties.
You found a part of Alpha Team, or at least what little was left of one of their members. Intelligence gained from their log book tells of a survivor base just outside a FEMA quarantine area.
You were able to evade capture by the horde of infected on your trail through demolishing the tunnel system you used to escape. Your only option is to press onwards to find what is left of Alpha Team and get home alive.