Ever since Gertie Milk arrived on the mysterious island of Skuldark, she's felt like something was missing. According to Kolt, her mentor and fellow Keeper of Lost Things, the island used to be filled with other Keepers. But now Gertie and Kolt are the only two people left (or two and a half, if you count Robot Rabbit Boy, their bumbling but lovable Series 7 Artificial Intelligence Forever Friend) who can return misplaced items throughout time. So when Gertie learns that the missing Keepers have been imprisoned by the Losers, their very evil adversaries, she knows she must make it her mission to rescue the kidnapped Keepers and return them to Skuldark. But that proves more difficult than she'd imagined, since her time-travel missions don't seem to be taking her anywhere near the missing Keepers. And it doesn't help that the Losers have an evil master plan worse than their last evil master plan, and this time the entire future of the universe is at stake. Fueled by more than a few delicious cakes and plenty of Skuldarkian seawater, Gertie, Kolt, and Robot Rabbit Boy must travel through time (and space!) to save their island home and rescue the Keepers who've been lost to history before the Losers manage to capture them all.