For the Double Blind step in the Exodus: Evacuation Exotic quest, you will need to complete the Unexpected Guests Heroic Adventure on Io. Normally Heroic Adventures are started by visiting their totem on the map and interacting with it, but for this quest things are a little different.
If you open up your Director, go to the Destinations tab, and look on the left side of the map for Io, you will find a blue symbol. This is actually how you begin the Heroic Adventure for this quest. We imagine the change was made because Bungie suspects that some players will not have unlocked the Heroic Adventures for Io, adding a lot of grind to the quest.
Click on the symbol in the Director, and the quest will begin. It is a pretty simple quest where you will be fighting plenty of Taken enemies. Head to the waypoint, then fight the Taken Psions that keep spawning in. These will spawn forever, so keep an eye on the top left of the screen for when the message changes, telling you to pursue the Taken.
Go down the tunnel at the platform to your left, and you will find yourself in front of a strange portal. You will need to shut it down by collecting energy orbs in the tunnels, so follow the waypoint to each orb, bring it back to the portal, and slam it into the ground beside it.
When you have collected all three, a powerful Taken Wizard will appear, and you simply need to kill them and the mission is complete, allowing you to move on to the next step in the quest.