The third book in the Dreamhouse Kings series by Robert Liparulo is called Gatekeepers. This book starts just where the book Watcher in the Woods ended. The King boys, Xander and David, are left on their own when their Dad has been arrested based on false charges and a few bribes paid out by the ancient assassin. Xander and David believe that they have made contact with their mother in a portal that takes them to a Civil War encampment near the front lines of battle. They left behind a clue that only she would recognize. When someone answers the clue, the boys begin to visit this period to find their mom. However, every time they enter into the portal that leads them to the camp, they barely escape with their lives.
Throughout, the King children continue to match wits with the mysterious assassin who is bent on killing them. Although the doors to their house are locked, he seems to have ready access whenever he pleases. We also learn that he commands several of the ogres who come and go through the time portals to carry out his bidding. We know his aim is for evil, but we don't yet know what is going on. Just when things start to close in on the children so that they fear they will have to flee for their very lives, the sickly old man Jesse arrives on the scene with his traveling nurse, a former army ranger named Keal. Keal knows how to take care of himself when needed. Jesse and Keal are just the allies that are needed when things look the darkest.
Before this book ends we learn that the DNA of the King family is somehow tied to the house of dark shadows. Their destiny is to live in this house and protect it, to act as the gatekeepers. Yet they feel overmatched. Just when they think they have found their mother, it turns out their have found their grandmother who was dragged away over 30 years earlier. Clues to the whereabouts of their mother, the path that leads to her, have completely vanished. While they rejoice in the return of their dad from jail and the rescue of their grandmother, Jesse tells the Kings that not all of the portals lead to the past. There is one that takes them to the future. It is through this door that they will come to understand the full impact of what the assassin has done to the past, and what inky blackness his wickedness has wrought on the future of humanity. Now on to the fourth book in the series, "Timescape".