In the novel it explains that the younger brother Nissos had brought Seria to the lake and left her there hoping she would basically disappear so when everyone found out what he did they went to look for her and their farther the Marquise was pis*** at Nissos so Cassius not wanting him to get in even more trouble had Seria been badly hurt went to look for her himself and when he found her he tried to hide her from their father by pushing her face into the snow not knowing there was a hole in the lake where her head was and almost drowned her
@Chanelle22 no, actually he intentionally tried to kill her, he wanted to make a "2 birds in one stone kind of situation", he knew he was holding her head under water, so much that she even struggled(as one should), and he only stopped because the butler arrived. Only him, the butler and his mother know of this and he'll try to harm her agai
