Whilst this story and its characters are fictional, like the others in the Sinclair’s Mysteries and Taylor & Rose Secret Agents series, this book takes some inspiration from real-life history.

For example, although the attack at the circus which appears in the story is fictional, the assassination of Russian politician Pytor Stolypin in a Kiev theatre at the start of the book was a real historical event. You may also spot some real historical figures in this story – from daring French pilot Elise Deroche, to British ambassador Sir George Buchanan – and of course Tsar Nicholas II and his family who, just six years after this book is set, met a sad end during the Russian Revolution.

Riviere’s, the elegant jewellers, is inspired by the real-life Fabergé, founded by master jeweller Peter Carl Fabergé and best known for its famous Fabergé eggs. Today St Petersburg is home to the Fabergé Museum where you can see many of the wonderful treasures that Fabergé’s jewellers made for the Tsar and the Imperial Court.

Although there was no real-life Circus of Marvels, circuses were popular entertainment in the late 19th and early 20th centuries. Large circuses such as the Barnum & Bailey Circus really did go all over the world on their ‘grand tours’, very often travelling by train. It was common for circuses to feature performing wild animals at this time, when attitudes to animal welfare were very different to ours today. At the time of writing, the use of wild animals in travelling circuses is banned in many countries, though not yet in the UK.

The Secret Service Bureau which appears in this story is (very) loosely inspired by the real Secret Service Bureau, which was set up by the British government in 1909. Initially very small, it soon grew and was divided into two divisions – one to deal with counter-espionage at home in Britain, and another focused on gathering intelligence abroad. Today we know these as ‘MI5’ and ‘MI6’.