The mold takes all. Twelve-year-old fairy Canary Mossheart knows this better than most. A few years ago, the mold took her papa, and even her famous, former-chosen-one Gran never found a cure. So when Ary's beloved mama falls ill, Ary decides it's taken enough. Armed with only a bucket and a prayer, she sneaks out to find a magical, underground lake whose healing waters are straight out of Gran's adventures. But when Ary gets there, the lake's bone dry, and instead of healing waters, she finds a terrifying secret: Her entire world is actually trapped inside a giant terrarium, one they were meant to leave centuries ago. Worse, Gran knew and hid the truth, dooming Ary and her generation to a dying, rotting world. Now, allied with only her doomsday-obsessed frenemy, a timid pill bug, and a particularly grumpy newt, Ary has one week to unravel the clues and find a way out of the terrarium, or they'll be trapped for good?