Luna and Alex are in a happy relationship while "A Canterlot Wedding" is approaching, what could go wrong ;-) This is a sequel. I strongly recommend reading "Moon's shadow" first
Much changes as Chrysalis moves into the library so our pair can "research" her and find a way for the changelings to fit into pony society. Meanwhile, a new threat emerges.
Stella finds a new world full of wonders, what starts as pure research becomes something life changing for her. There are stories with characters dance around each other and finding each other just at the end of the story... this is not one of them.