Ben is a plumbing obsessed fourteen-year-old boy, slowly getting used to life without his beloved cabbage-obsessed Granny around. She loved scrabble and was also an international jewel thief known as the Black Cat – the original Gangsta Granny, a secret that only Ben knew about.

When world famous treasures like the World Cup, the Mask of Tutankhamun, and the Queen's Wax Figure at Madame Tussaud's are stolen and the clues point to none other than the return of the Black Cat, Ben doesn't know what to believe.

Mr Parker, head of the neighbourhood watch, accuses Ben of being the new Black Cat and has him thrown in jail. Linda and Mike, Ben's parents are ready for their big night at the International Ballroom Championships hosted by none other than the fabulous Flavio Flavioli, until Mr Parker runs over Mike's foot with his mobility scooter. Desperate for a dancing partner, Linda convinces the police to release Ben and takes him to the Palladium to dance with her in front of the Queen.

After the dance goes horribly wrong, Ben escapes through the theatre and follows a figure dressed in black, could it be the new Black Cat? He follows them to the roof and sets in motion an adventure through night time London to clear his name and discover who has been impersonating his Granny.