Double trouble squared

July and Liberty Starbuck, twins, and their family are busy exploring the streets of London where their father has accepted a new job. A voice that only the twins can hear needs their help. In their efforts to provide this, they use their individual talents, to include telepathy, to uncover a heretofore undiscovered manuscript of Sir Arthur Conan Doyle, along with the ghost of the forgotten twin brother of Sherlock Holmes.