Sherlock Holmes has retired. After a cruel accident during a fruitless chase for Moriarty, Holmes is maimed badly enough that he declares he will no longer solve the crimes of the London streets. But then a letter comes. A letter imploring him to investigate the Opera Populaire's ghost. The spectre everyone has heard rumours of, but only one has seen.

Erik has returned and has brought an interesting character to Holmes's attention: Dr. Henry Jekyll. It appears Jekyll is experimenting on an unsanctioned patient in an effort to prove his theories concerning human nature correct. But who is the patient he's found? Is it his mentally ill father, shut away for years in an institution? Is it Simon Stride, the jealous former suitor of Jekyll's fiancee? Or could it be the mysterious, unsavoury murderer, Edward Hyde, with whom Jekyll seems to have intimate knowledge? Sherlock Holmes, along with Erik and Watson, investigates this bizarre case....