New primary objective: Speak with Gabriella
Look for Gabriella in the Dark Brotherhood's Sanctuary and ask her about the details of the new task (screen above). You'll learn from her that there are currently preparations for the visit of the Emperor and some of them consist of checking the security of major settlements in Skyrim. Gabriella wants you to assassinate Gaius Maro, son of commander responsible for security. But that's not all. She also wants you to plant an incriminating letter on Gaius's corpse. It is worth noting that you can get a bonus if the indicated person is killed in one of the settlements he is visiting and not during his journey between towns.
New primary objective: Kill Gaius Maro
New optional objective: Steal Gaius Maro's travel schedule
Leave the Dark Brotherhood's Sanctuary and open the world map. A person you're supposed to assassinate will start his journey in a small settlement called Dragon Bridge, located in the northwestern part of Skyrim (screen above). If you've already unlocked this location, you can use fast travel option. Otherwise start your travel in Solitude and then choose a main road leading west.
Once you get to Dragon Bridge, move to the Penitus Oculatus Outpost area. You'll witness there a farewell conversation between commander Maro and his son Gaius, who is going to check major settlements in Skyrim (screen above). If you want to finish the quest as soon as possible, just wait until Gaius leaves the town and attack him on the road, but it is better to complete additional Gabriella's request and kill him in one of the major settlements.
Stay in Dragon Bridge and enter the Penitus Oculatus Outpost. If you do not want to kill anyone here, you can only take a look at Gaius Maro's Schedule lying on the table (screen above). These are its contents:
- Morndas - Solitude, Emperor's Tower
- Morndas evening - Solitude, Castle Dour
- Tirdas - Windhelm, Palace of the Kings
- Tirdas evening - Windhelm, Barracks
- Middas - Riften, Mistveil Keep
- Turdas - Whiterun, Dragonsreach
- Turdas evening - Whiterun, the Bannered Mare
- Fredas - Markarth, Understone Keep
- Fredas evening - Markarth, guard tower
- Loredas & Sundas - Markarth, the keep
If you want to take a schedule with you, make sure that there is only Penitus Oculatus agent left in the room. You can wait until he walks away and steal the schedule or perform a quiet execution on him, sneaking behind his back.
With the schedule in your hands, you can now plan your main actions. The goal is of course to appear in the right place at the right time. Remember that a current day of the week can be checked in the world map or by pressing T key (screen above). Your further moves must be planned ahead so that after reaching the city you can meet Gaius Maro there.
I strongly advise not to attack Gaius during the day, because he visits almost only public places, so you would be immediately surrounded by local guards. So you should ambush him by night. In this case I do not recommend the cities, where Gaius stays for a night in the castle or in barracks, because in such places there are other guards and this fact practically prevents silent assassination.
In my opinion it is best to wait for Gaius in Whiterun, in the Bannered Mare inn (screen above). Commander's son will appear there at Turdas evening (I suggest using sleep option to speed time).
The man should spend a few hours in the main inn chamber, but sooner or later he will go to the guest room and lay down to sleep (screen above). Crouch and carefully enter this room, closing the door behind you. Approach Gaius and attack him. It is worth noting that he is very tough, so you should better equip a good dagger or a bow. Otherwise a surprise attack won't kill him, but only wake him up and you'll have to not only fight him but also will alarm other guests in the inn.
New primary objective: Plant the Incriminating Letter on Gaius Maro's body
Regardless of how and where you assassinated Gaius Maro, you have to approach his corpse and interact with it. Open your inventory, select Books section and mark a position named incriminating letter (screen above). Now press R key to move this object to Gaius's inventory. You can now close this window.
New primary objective: Report back to Gabriella
Make sure that you're in place where you can start fast travel and journey to the Dark Brotherhood's Sanctuary. Once you get there, Gabriella will run up to you. You have to report her about your mission (screen above). As a reward you'll receive gold and Olava's token, which can be used to meet local fortune teller (sidequest). Gabriella will send you to the main chamber of hideout, informing you about crisis situation connected with Cicero.
The Dark Brotherhood unlocked quest: The Cure for Madness
The Dark Brotherhood unlocked quest: Miscellaneous: Receive a reading from Olava the Feeble