This page of A Plague Tale Innocence has a walkthrough for chapter 11 - Alive. This short chapter takes place in Chateau d'Ombrage. Read the walkthrough to, e.g. learn how to ask Rodric for help, or how to reach the main hall.
First, ask Roderick to break the door. Proceed through the narrow corridor. It will lead to the next door, which also have to be opened by force. Thus, you will get to the yard. After a short conversation, you will have to follow for Lucas to the main lobby.
After the cutscence comes the end of the task.