You discovered that the plain looking book was actually something much more. This magical book is actually the The Book of Varik, founder of the Druid Order. Finding a magical incantation hidden inside the book, you stumbled upon a way of transporting yourselves to a different plane of existence. Here in this other plane, you met Varik and learned some dark secrets of the Kingdom of Kalinor and about its true history. It was revealed to you that the Goblins were good, peaceful people and that in actuality it was the men that were evil and warmongering.
Varik said that he would be able to help you with more information later, but warned that continued traveling between the planes would result in losing a part of yourselves.
When returning to the normal plane, you saw a group led by the man you delivered the box to laying an ambush. They were unprepared for the burst of energy when you arrived. You defeated them, and the shady man vanished just as the killing blow would land upon him.