Amelia and William spend a lot of time in the library, and that's where they plan to spend most of the summer holidays. But things quickly change when an old piece of paper falls out of a book Amelia takes from the shelf. As they work together to solve the mystery on the paper, an adventure begins across London in search of a hidden treasure - but they are not the only ones looking for these jewels. Amelia and William must put their knowledge of London and British history to the test as they solve clues hidden throughout the city, and they must think fast as dangerous forces close in...