Sherlock Holmes, Arsene Lupin, and Irene Adler meet up in London only to find a strange chess problem in the Times signed by "The Black Friar." It's written in an unknown code which Sherlock is eager to solve. The next day, the city is rocked by the news of a rich merchant found murdered. On the merchant's desk was scarlet rose: the same flower used as the calling card for a brazen criminal group that haunted the streets of London twenty years ago. Could the Scarlet Rose Gang be back?

Irene's family has moved to Evreux, Normandy. Soon after arriving at her new home, she is approached by a mysterious woman who mutters some strange words about Irene's mother being in danger, before vanishing into thin air. It's just the first in a series of unsettling events that Irene, Sherlock, and Lupin must decipher. The three sleuths questions will lead them to a secret crypt far beneath the streets of Paris and to an ancient relic that it is rumored to be worth a fortune. But how far will someone go to obtain the priceless treasure? Secrets and twists await the young detectives at every turn as they solve the case of The Cathedral of Fear.

While on summer vacation, little Irene Adler meets a young William Sherlock Holmes. The two share stories of pirates and have battles of wit while running wild on the sunny streets and rooftops. When Sherlock's friend, Lupin, joins in on the fun, they all become fast friends. But the good times end abruptly when a dead body floats ashore on the nearby beach. The young detective trio will have to put all three of their heads together to solve this mystery.

Irene Adler, Sherlock Holmes, and Arsène Lupin planned to reunite in London, England, for their second adventure together...but Lupin doesn't show up. His father, Théophraste, has been arrested for the kidnapping of a famous opera singer and the murder of a secretary to the great composer, Giuseppe Barzini! The three intrepid detectives start a full investigation to clear Théophraste's name and rescue the missing soprano, Ophelia Merridew, only to discover that the singer is being held captive by criminals in the deadly district of Bethnal Green. Join Irene and her friends in their twist-filled bid to solve the mystery of The Soprano's Last Song.