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You are dropped of at a dark swamp. You should see another Pelican in the distance. Walk to it. If you're playing on easy mode you should find some shotguns nearby. If they are there pick it up. If not, continue on ahead and there will be some covenant. After that try looing around for a covenant dropship lying agaist some rocks. Go around it and you should find some jackals. After you take them out you should see a root-like thing. Its a bridge so go across it. Yous should see some stationary guns and some assault rifle fire when you come closer. Ignore that and continue on. You should see a grav lift. Go down and try to find a room. There's full of covenant blocking it so you could just melee them out of your way. You should find some more covenant, still the usual grunt and jackal. It will be ver obvious where to go from here. Try to find doorswith green lights on them. You might find a crazy marine with a pistol along the way shooting at you and babbling stuff. If you find him annoying, just whack him out of his misery and move on. You should find some weapons laying around the room the crazy marine was in. If you find a plasma rifle, pick it up in exchange for you're assault rifle. Hopefully you finally reach a room where you go down in the middle of it. Heres the cutscene.