Light at the End of the Jungle begins when you talk to a woman about her husband. She'll ask you to watch him because she thinks that he is cheating on her with another woman. She thinks that the lord will forgive him, but only if he comes clean.
Locate Rebecca's husband.
Get close to overhear the conversation.
Return to Rebecca or confront her husband.
On the other side of the street is the building with her husband in it. If you don't get to the window quickly, a countdown will begin at the top of your screen before you lose the mission. Get the window to hear into their conversation.
You'll realize that her husband was cheating, but not with a woman. You are then given a choice; go confront the husband, or go tell the wife.