The Replicated Man Fallout 3 Walkthrough (Side Quest) - Guide by Carl
Craterside Supply, Megaton
Clinic, Tenpenny Tower
Saint Monica's Church in Rivet City
Zimmer wants you to find his android so that he can recover it. You have multiple options for completing this quest, both good an evil. The rewards differ quite a lot between the two choices. The simplified version of the rewards is: Wired Reflexes: Zimmer will give you this if you give him the information he needs about the android. The perk adds +10% chance to hit in VATS mode. This is the clear choice if your character won't even be using energy weapons.
A3-21's Plasma Rifle: This gun is awesome. It's a modified plasma rifle that does more damage than usual, crits more often and is more durable. To boot, it can be repaired with standard plasma rifles. The downside is that if you get this early in the game, you won't likely be repairing it any time soon because plasma rifles are not very widely available until the Enclave appears in the Wasteland after The Waters of Life. If you want both rewards, it's entirely possible but involves a bit of double crossing.
Before we get to the options once you have the information about the android, we need to learn a bit more about him. To do this, talk to Dr. Preston in Rivet City's clinic after starting the quest. You may need to pass a speech check or bribe the doctor, but afterward you will get a note that you can listen to. Afterward, go back to the main entrance and through the door to the midship deck. You'll be looking for Saint Monica's Church. Inside, look behind the pulpit to find a holotape on the shelf there. There's also an empty whiskey bottle, hmm. Anyway, grab the holotape and listen to it to learn of Pinkerton, who is the guy who did the memory wipe on the android.
If you've done the Wasteland Survival Guide, you should already know how to get to pinkerton. If not, know that he is in the other half of the broken ship that became Rivet City. There is a door that can be lockpicked to get inside, but it requires 100 lockpicking. The alternate way is to go underwater by the broken side and through the hazardous area to reach the Dr. Be sure to save your game before you attempt this method as it is quite dangerous as there is radiated water, explosive gas, and mirelurks. But all in all, it's a worthwhile endeavor.
Once you reach Pinkerton, drill him about the android. Ask him for proof, and when he gives you the password to his computer let him know that you're sure there's something he's not telling you. He'll give you the secret code he put into Harkness to reactivate his memories. Once you have all this information you can choose among your options.
Good Options (A3-21's Plasma Rifle): Talk to Harkness. I found him in the marketplace around 1pm, he may wander. Show him the evidence that he is an android, then reactivate his memory. You can choose to let him kill Zimmer, or have him force Zimmer off the ship. Either way you'll get good karma here as well as the Plasma Rifle.
Evil Option (Wired Reflexes Perk) Go straight to Zimmer with the information and tell him that his android is Harkness. You'll receive wired reflexes.
Getting Both Rewards: Tell Harkness that he is an android, then ask him what he'll do about Zimmer and ask if you can have the pleasure of killing him. Then go to Zimmer and tell him about Harkness, then pop Zimmer in the head. You'll get both rewards this way!