How does John's hunch pay off when he meets Angela Harding?

When John meets Angela Harding, he has the feeling that Karen had seen, or was planning to see, Angela the day she died. Playing on this hunch, he claims that Alan Zenner told him that Karen was headed to Angela's apartment on Sunday. Judging by Angela's angry, shocked reaction, which she quickly tries to hide, John realizes that his impression was right. His hunch pays off by giving him more pieces of the puzzle.