Main missions are visible on the map as hexagons. They lead you through the main story. The stationary ones remain as a grey hexagon after completion so you can experience them again in different difficult settings.
Grand Washington Hotel
Rendezvous with Agent Kelso and stage a daring assault to rescue Eleanor Sawyer from the Hyenas.
Theater Settlement Mission
Jefferson Trade Center
Reactivate the ISAC node beneath the center and rescue the missing Division agent.