Time has passed since the events of Book 1, and tween orphans April, Sadie, Colin, Tim, and Violet should have happily settled into life at the WINTERBORNE HOME FOR MAYHEM AND MYSTERY, under the protection of their new guardian, eccentric billionaire Gabriel Winterborne. Who, unbeknownst to everyone but the kids, is also the local, sword-wielding, caped avenger The Sentinel, who comes to the rescue in perilous moments. However, things are running off the rails fast, as Gabriel is completely undone by the disappearance of Ms. Izzy Nelson, his love interest, who everyone hopes will marry Gabriel so that they can all be a family. Adding to the trouble: Butler Smithers, who helped keep order around the place, won an around-the-world cruise, and is temporarily but definitely away. Things get worse when a formidable, pencil-wielding woman from Child Protective Services shows up amid the chaos and seems determined to break up their happy home -- the only one most of them have known. Then Gabriel disappears, leaving the kids to fend for themselves. Violet, the youngest, is sure he's coming back to save their family. April, who waited 10 years for the mother who left her in foster care and said she'd be back, isn't so sure. Meanwhile, the lady with the pencil isn't giving up, and a rich guy who claims to be a friend of the absent Izzy is working very hard to make the kids like him. The shadowy forces responsible for murdering Gabriel's whole family in the past are still in the picture. Then there's the fact that the absent Gabriel may not be the only Sentinel out there. It's a lot to cope with, but the kids have skills and a strong bond.