A Two Story Job

 is a side quest in.

Synopsis
Lord Reymont is the wealthiest man in Brackenbury, who recently procured an unique jewel the Heart of the White March. Abrecan Doemenel plans to acquire it, to ensure that neither the Crucible Knights nor the Dozens can buy it and return it to the original dwarven owners in the White March, gaining a powerful ally and thus upsetting the delicate balance of power in the Bay.

Walkthrough
There are two ways to receive this quest. The first is by entering an unmarked house in the northeast of the Copperlane where thieves will attack you. One of them has a Thieves' Letter which allows you to start the quest. You can give it to either Lord Reymont or to Abrecan Doemenel to proceed.

Alternatively, you can receive the quest directly from Abrecan Doemenel himself. This requires you to have been referred to him by his sister Danna during At All Costs after helping her kill Verzano. If you received the quest this way, Abrecan sends you to get him the letter from the thieves, preferably without violence. Again you can decide whether to return it to your employer or to show it to Lord Reymont.

If you return the note to the Doemenels, you are then tasked with stealing the Heart of the White March from the Reymonts. The easiest way to do this is to enter Reymont Manor through a second floor window, left ajar by an insider contact. Use a Grappling Hook or climb up the wall (Athletics 3 for all party members required) to get inside. Move along carefully through the adjacent corridor in Scouting Mode, and you should discover a hidden switch opening a false wall. Inside the secret room, a trapped (level 8) chest has the gem. Be careful in the corridor, as guards patrol the area. Once you have the "Heart", exit through the window and return to Doemenel Manor.

If you deliver the letter to Lord Reymont he will give you 2000 and a Ring of Unshackling. You will also receive moderate negative reputation with the Doemenels.

Bugs

 * (v3.7.0.1318) If you acquired the Thieves' Letter, stole the Heart of the White March and progressed far enough in the main quest where you can ask out Abrecan Doemenel about House Doemenels interests in the Animancy Hearings, you can get stuck when speaking the first time to Abrecan Doemenel and directly starting the topic "Invitation to the hearing in Duc's palace" without scratching any other topics concerning the Thieves' Letter - You end up being unable to mention the (now successful) acquirement of the letter nor handing over the diamond. Dialog window will simply get closed if you try to do so. You still can end the quest by talking to Lord Reymont. Needs to be verified further