One girl is about to discover that a day doesn't just disappear... it gets stolen. Alma’s morning starts all wrong. The air in her house is cold and still. The warm, sweet, mapley smell of her mom’s famous Wednesday-morning pancakes is missing. Her fuzzy blue socks are gone. Then, the real wrongness begins. Her mom insists it's Tuesday. Her best friend Sam's birthday party, which Alma knows is today, has been forgotten. When Alma races to her room, she finds the most terrifying clue of all: her diary, always filled with her drawings and secrets, has a bright, white, perfectly blank page right where Wednesday should be. whole day hasn't just been forgotten, it's been stolen.

Alma's desperate search for the missing day pulls her into a world hidden just between the seconds of a clock. She follows a trail of impossible backward-footprints, discovers a magical shop that sells lost moments, and hears whispers of a shadow who creeps into the world to un-spill milk and un-ring bells. She must follow the clues to the Land of Last Week, a place of faded colors and a thousand mismatched-ticking clocks. There, in a castle built of time, lives the Yesterday Thief a lonely, sad hoarder who captures precious moments in glass jars to "keep them safe." Now, Alma is the only one who can fix the present. But to get her Wednesday back, she'll have to confront the thief and convince him that days are for living, not for keeping. Can she save the stolen day before it fades away forever?