In the spring of 1932, with Londoners terrorised by a series of brutal murders, the private detective agency of Messrs. Singleton and Trelawney quietly opens its doors in Bloomsbury.

The first person to call on their services is a worried Lady Arthur Conan Doyle. She tells of mysterious events at 221 Baker Street - and a premonition that the London murders signal terrible danger for mankind.

Their investigation will take our intrepid heroes into a world of séances and spirits. Aided by the most famous detective of all time, they must draw on their knowledge of the imaginary to find the perpetrators of some very real and bloody crimes before they strike again...