From Destinypedia, the Destiny wiki
The Guardian heads toward the entrance of the old subway station, which has Taken emerging from it. They move on, into the pitch black darkness of Freehold Station. A horde of Taken, including Minotaurs, have infected the area. The Guardian kills them all and heads deeper inside. More Taken await the Guardian in the tunnels, including Hobgoblins and Centurions. They quickly deal with the enemies and reach the Tharsis Junction.
The Guardian continues down the tunnels, past the abandoned trains and dormant Vex gates. Upon finding a large group of Taken, they discover a large hole in the far wall. Even more mutated infantry spill into the area. The Guardian continues investigating, and they are surprised to find the entrance to the Black Garden.
The Guardian continues exploring the Garden silently. Eventually they turn a corner and find themselves face to face with an Echo of Oryx. It disappears immediately and drops a few Taken soldiers in its place.
The Guardian defeats the soldiers and continues ahead. The Echo is waiting for them around another corner. Like before, the Echo disappears and leaves more enemies in its wake. As the pattern forms, the message becomes clear: The Echo is leaving behind a trail for the Guardian to follow. Eventually, this leads the Guardian to the inner workings of the Black Garden. All across the vast landscape, several Taken portals sit scattered around the once pristine oasis.
The Guardian finds the Echo, floating in front of a Vex gate. Upon making contact with the Guardian, it disappears. The portal closes behind it, and a Taken Lieutenant steps out. Surrounded by Centurions and Hobgolins, the Guardian fights and eventually kills Bracus Sho'ogurn. The remaining Taken retreat.