WARNING: If you attack and kill Astrid, the entire quest line will close to you and you will not be able to get this achievement, 'Bound Until Death' or 'Hail Sithis' on this playthrough. Complete the mission (you can't make a wrong choice-I chose all three and received accolades for it) and the achievement will pop. After that, go to sleep in a place OTHER THAN Windhelm, and the 'With Friends like These' quest will begin when you wake up. After some days, the Dragonborn received a mysterious note with an imprint of a black hand and the words We Know written. Upon completing Innocence Lost, you will receive a message from a courier.
You can speak to them to gain additional information, then follow up by entering the house and talking to Aventus, which will trigger the 'Innocence Lost' quest. Before entering the residence, you will overhear a conversation outside between Grimvar Cruel-Sea and Idesa Sadri, and they will be discussing what Aventus Aretino has done. The first city guard you speak to should mention a 'curse' and direct you to the Aretino residence. To start this questline, travel to Windhelm. This achievement is obtained after completing the first Dark Brotherhood mission.
