Describe what happens when the figure of the killer appears to Harry outside his apartment in chapter fourteen?

The figure appears and admits that he is the one that sent the demon and that killed Tommy Tomm and Jennifer. The figure won't give his name and appears to be powerful but is shocked when Harry probes out with his senses to find out about the figure. The figure is also shocked when Harry is able to blast him. Harry realizes that this person is powerful but has no knowledge of common wizarding practices.