Valentine comes home and receives the warmest of welcomes from his daughter: "I wish you'd died in the mountains" (30.9). Yikes. He wasn't expecting that.
Katherine pressures him into telling her what really happened with Hester's family.
Not only does Valentine admit to killing Hester's parents, he also admits that he might have been Hester's father: that's right, Hester and Katherine might be half-sisters.
Valentine tells Katherine that he did it for her, so that she could have a groovy London lifestyle.
Frustrated at her father's lack of remorse, Katherine realizes she has to take matters into her own hands and stop MEDUSA herself.