A Manhandled Manservant

 is an unmarked Fallout 3 quest.

Receiving and completing the quest
Argyle has not been seen since he was separated from Herbert "Daring" Dashwood on their escape from Rockopolis. The retired adventurer refuses to believe his manservant died in that battle though, instead believing he is still out there somewhere. Upon visiting Rockopolis and finding Argyle's corpse, the player may return the news to Herbert Dashwood at Tenpenny Tower for a reward.

Dashwood, sad to hear of Argyle's demise (he always thought Argyle would outlast him by at least 100 years), tells the player that his days of adventuring are over and gives the player the key to his safe.

Rewards
Inside the safe are Bottle caps, Mentats, a Mini-Nuke, Rad-X, Schematics - Bottlecap Mine, a Stealth Boy and Stimpaks.

Taking any of these will result in him saying "thief" and becoming hostile, along with any guards that witnessed you stealing.

Bugs

 * You can take all the caps in the safe and Dashwood will not become hostile, provided he has given you the key.
 * Even after receiving the key, taking any items from Dashwood's safe may be considered stealing, resulting in Dashwood taking the items back if he sees you use the safe. This can be avoided by waiting for him to leave the room, though it will still affect karma.