Once the hordes have been suppressed and Demeter lies dead, your team will decide to take Charlie to the Science Labs in Apollo. You may proceed there whenever, but now is the only time to complete optional missions and gather supplies before numerous hordes and bosses. Be wary when traveling, and stick together. Agrons and Devourers patrol the map, and Wraiths travel the skies. Weaker classes should stick close to the remnants of the security team.