The second part of the story needs to do some or all of these four things, I think.

• It needs to have a cool twist, or at least an interesting pay-off to the main plot point - a way of using the "magical" effects of Then! which is surprising or arresting or frightening.
• It needs to have some sort of resolution for Paul himself. What we've learned about him so far has mostly related to his wife walking out on him, and to a lesser extent to his mother's insanity and death. A second half that refers back to these things, and leaves Paul in a different place from where we found him, would be good.
• It could also explain the shadowy figure in the garden and the drop of blood on the dog rose.
• . . . . and it could contain some revelation about the mysterious Abanaazer Krohl; who he is or what his agenda is or why he's chosen to approach Paul in this way.

If I was finishing off the story myself, these would be my starting points.