"If it hadn't been for you, Camille's plan would have succeeded."
On the way to Anderson Mansion earlier, Yvonne had explained how she'd discovered the aconite powder in the medication. Since she had to keep her medical skills a secret, she made up a story claiming that she'd mistakenly consumed aconite as a child and had almost lost her life. Hence, she vividly remembered its smell and taste, which had inadvertently saved Stephen.
Philip looked at Yvonne with warmth and said, "Thank you, Yvon