Mimi adores her wild, fun, full-of-life gran. Then Gran starts forgetting things. Suddenly there are cracks appearing all around their home - and a mysterious black crow - both of which only Mimi seems able to see.

Mimi is determined to solve the mystery. Luckily she has new friends to help: Titch and Nusrat. Together, they're the Stickleback Catchers: solvers of puzzles and seekers of adventure.

Down by the river, where the gang meet and the silvery sticklebacks swim, they discover a mysterious stone, speckled with stars. But this is no ordinary stone: it's the doorway to another world, a world of talking crows and secrets, magical constellations and memories - and maybe, just maybe, Mimi's chance to bring back Gran forever...