After returning from holiday, Luke and Lexi find a beautiful white mouse in their luggage. Strange to begin with, but to their shock, he can also talk and claims to be descended from a Hollywood film star, embarking on a Grand Tour of Europe from his home in Los Angeles.

Luke and Lexi persuade their parents to let him stay as their pet and after an eventful first night, they visit Aunty Rita, who, with her background in fashion, creates Algernon a wonderful wardrobe of clothes ready for his trip. 

It seems the perfect arrangement - but Algernon creates havoc wherever he goes and has a problem with boasting about how fantastic himself and his family are. What more adventures lie in store as the family embark on his Grand Tour with him? What trouble will they get into next?