"Dark Corners"

Books: I listened to the audiobook “Dark Corners” by Ruth Rendell. From Goodreads (here):

When his father dies, Carl Martin inherits a house in an increasingly rich and trendy London neighborhood. Carl needs cash, however, so he rents the upstairs room and kitchen to the first person he interviews, Dermot McKinnon. That was colossal mistake number one. Mistake number two was keeping his father's bizarre collection of homeopathic "cures" that he found in the medicine cabinet, including a stash of controversial diet pills. Mistake number three was selling fifty of those diet pills to a friend, who is then found dead.