Brave, clever and never more than a whisker away from adventure! When the museum's visitors are gone for the day, it's time for the cats to come out to play? When the kittens overhear their enemies, the rats, whispering about a treasure map hidden in the museum, Boris is especially excited. Could the map belong to the legendary pirate queen Diamond Nell, whose ship - The Silver Lion - is on display in the museum? And can they stop the rats from getting their claws on the pirate's gold first? The fourth in a charming new series from Holly Webb. Purr-fect for fans of the OTTOLINE books and THE ROYAL RABBITS OF LONDON.