This is the second mission that Renko is given. While he is exploring the island Renko is sent back in time and the location he is at is on fire. Renko finds a man hanging for dear life trying not to fall into the flames. Renko saves the man and puts him on his shoulders. Escort the man through the firey building and get down to the bottom level where he will be examined by doctors. Renko is sent back to the present and the mission is complete.
In truth this is the single most important mission in the game. To found out why you will have to see the ending.