Double trouble squared

Twins July and Liberty Starbuck arrive in London with their family, following their father's move there for work. Eager to see the city, they roam its streets until a voice that only they can hear asks for their aid. Drawing on their own special abilities, including telepathy, the pair set out to answer the call. Their search brings to light a previously unknown manuscript by Sir Arthur Conan Doyle and the spirit of Sherlock Holmes's long-overlooked twin brother.