When a highly dangerous new arrival goes missing, the race is on to catch it before disaster strikes. Discovered in the Unknown Wilderness when she was just a baby, Indigo Wilde was adopted by World-Famous Explorers, Philomena and Bertram, who are always off adventuring. Home for Indigo and her little brother, Quigley, is 47 Jellybean Crescent, a crazy and colourful house full of magical creatures that her parents have taken in over the years. There's Fishkins a purrmaid half-cat, half-fish, and always grumpy; Graham, a llama-corn with a particular taste for tinsel; Olli and Umpf bright pink and blue yetis who can't blend in to the snow, and that's to name just a few of the creatures. And now Indigo's parents have sent another Monster Mail delivery to Indigo and Quigley. But this time, the box is empty, and the escaped creature is running rampage around the house. The race is on to catch the creature before it's too late.