How does the Shadow Soul familiar work? I understand what you can do with it before the hero begins his turn, but then do you get to move Shadow Soul again at the end of the hero's turn to any empty space within 5 movement point's in accordance with the general rules for familiars?

You sure do.

First, the hero decides to do one of 3 things at the beginning of his turn:

1. swap with the shadow soul

2. bring shadow soul adjacent

3. do nothing with shadow soul.

Then, at the end of the hero's turn who has the shadow soul as his familiar, he may move the shadow soul up to five spaces, following the rules for movement of a flying figure, not ending in a space occupied by another figure per the rules of the shadow soul.

It's still a familiar, and follows familar rules for "activation," it just that it's special power happens to activate at the beginning of your turn. A very handy thing to do is send your shadow soul off towards a faraway door that you have opted not to open yet, then switch with the shadow soul, declare a run, and get into that next room to activate/retreat through a glyph so that the rest of the party can instantly teleport there. Major time saver in the bigger maps. Especially handy when used in conjunction with acrobat/zyla.