The night Louis was attacked.
As the man dragged Louis into the room Liza had been there speaking with one of the doctors her husband trusted. Her eyes widened seeing Louis, as the other doctor yelled at the man for having attacked a Moriarty brother. But the damage was already done, and they may as well dispose of him. But Liza had a different plan. She insisted using her new drug on the poor brother to keep him alive longer. Little did the attacker realize. She meant to keep Louis alive completely.
Having gained minor control over Edwin's doctor accomplices, she used those doctors and her own medical knowledge to operate on the semi-conscious Louis. Louis had lost a great deal of blood from the stab wound, and some internal damage. The attacker left her and the two doctors to take care of Louis.
"We need to clean the wound, remove the damaged tissue here. And close it. As for his face. Anything you can do for that? She questioned as the doctor operated on Louis and she kept forcing the young blond to drink her strange mixture. Louis seemed just barely conscious but kept struggling best he could. Liza knew if the scar was gone, and maybe a few other alterations. His brothers would doubt his authenticity. And that would make them easier to catch. Once she had all three brothers, she could use them for her own plans.
"I can make his scar less noticeable. Not fully gone. But to the point no one would notice unless they are looking for it." One of the doctors said as he began to cut at Louis' cheek. A mix of blood loss pain and the medicine caused Louis to finally lose consciousness. Once the operation was complete Liza sent for one maid to clean up the mess and had one the doctors take Louis away to his personal office. "Do not return him home until he has fully recovered. And keep it a secret what we have done." Liza ordered the man as he carried away Louis.
A mixture of drugs, and Liza's control by the time Louis was returned to the Moriarty manor caused the youngest Moriarty brother to have no recollection of what had happened to him. Enfact. For the first few days home, his mind was more foggy, cause him to barely even know his own name at times. This, with Moran's report from the maid, and the missing scar had caused Albert and William to believe this was not Louis.
The night of the tea party
However. The night Edwin died, as Louis laid in bed sleeping. William saw something. Though practically invisible, a faint outline of Louis' scar was still present on his right cheek. Realizing it truly was his brother William sighed in relief. "Welcome home, brother." He whispered softly with a slight smile. watching Louis sleep. Though, explaining what he saw to Albert. May be a bit hard.