Go to Paradise Survival Camp | Chapter 3 - The Ritual DI Riptide Guide

Attention - Before you make a decision of going to Paradise Survival Camp, prepare REALLY WELL, because you'll begin the biggest battle so far. Repair weapons, buy med-kits and other supplies. You can get there using Fast Travel (poster on the ground floor of the main building). When you get to Paradise Survival Camp, go to the main square what launches a cut scene with Marcus Villa and begins a huge battle caused by an attack of Horde.