Print all the pages in the same level in a book
This should work out of the box if you add the book navigation block to a region.

EDIT:

Sorry, I didn't realise that I was on on of the book pages so the book block expands in this case but not on non book pages. The way around this is to use Menu Block and create a menu block that starts at your About Us. Make sure you go into the advanced options of the menu block and select Expand all children of this tree.