Our Little Secret

Our Little Secret is an unmarked quest in Fallout 3.

Detailed walkthrough
Talk to Old Man Harris, who will warn the Lone Wanderer to get away from the town. After talking to Harris, head to the garden shed or the basement of the Smith's house.
 * Both doors are Very Hard difficulty (Lockpick 100). Picking either lock will give negative Karma.
 * It is possible to get the keys by pickpocketing either male adult, Bill Wilson or Jack Smith. Because they are evil, one will not lose Karma.
 * There are also keys in Smith and Wilson's houses on the nightstand next to the queen bed. One will lose Karma for stealing them.
 * There is a second key in the Wilson's house on top of the radio in the living room. Karma will be lost for stealing it.

In the basement or shack, the player can look around and discover that "strange meat" really is human flesh.

Upon exiting the area, the player will be confronted by the residents of the town, with the exceptions of Junior, Jenny, and Old Man Harris. Jack Smith will engage the player in conversation and ask if he/she saw anything unusual. If Old Man Harris wasn't spoken to first, and Lockpick was used to open the door during the day, they will immediately attack.

There are two speech checks in the dialogue tree. The first speech check option is to tell them that the Wanderer thought about "getting a snack." Having the Cannibal perk changes this to a guaranteed success. If one chooses to initially play coy by not answering straight, they will get another, easier speech check in the form of passive acceptance of their behavior (though this option will cause unintended issues). If one is successful at either speech check, in essence insisting that they did not see anything wrong and agree to keep their secret, the townsfolk will be kind to the Wanderer and Linda Smith will offer a free strange meat pie daily.

On the other hand, if the Lone Wanderer refuses to keep the secret, the residents will become hostile and attempt to murder them, forcing the player character to kill them all. Afterwards, the player can proceed to Old Man Harris' house. He will then tell more of the town's history and will agree to help raise the kids right.

Bugs

 * If the player character non-violently resolves the confrontation by selecting the line "Sure, Jack. No problem at all. I saw nothing." without having the Cannibal perk, the four parents will stand with their weapons drawn outside the shed or the house basement forever. The kids will disappear, and Old Man Harris' house will become key-locked. Even though they're stuck, one will still be able to get a daily strange meat pie from Linda Smith. This appears to happen with any non-violent resolution if Old Man Harris wasn't spoken to at all.
 * Picking "Yes, and I saw what you're hiding in there, you sick bastard!", then picking "Huh. Well, everyone's got to survive in their own way, I guess." may bypass this issue.
 * Arriving at Andale, one may encounter the families already gathered in front of the Smith house with their weapons drawn. Mr. Smith confronts the player as if they have already been in the basement. If one chooses to fight, they can loot the house and shed key from the corpses without Karma penalty.
 * After exiting the shed, Jack Smith will engage in dialogue with the Lone Wanderer, but it will be as if they have already negotiated with him. This means his dialogue options will be "What's wrong with that Harris guy?" etc.
 * When inspecting the Smiths' basement and then leaving the home, the town's adults will be gathered in front of the shed with their weapons drawn but will talk to the player normally and walk around. Jack Smith will not approach the player, but speaking to him will begin the dialogue about what the player saw in the basement.