While on summer vacation at the seaside, twelve-year-old Irene Adler meets the young Sherlock Holmes, and his friend Arsène Lupin--and when a dead body floats ashore the three young friends set out to solve the mystery.

Whisked out of Paris ahead of the Prussian army in 1870, twelve-year-old Irene Adler is reunited in London with her friends, Sherlock Holmes and Arsène Lupin--but Arsène's father has been arrested for murder and the kidnapping of a famous opera singer, and it is up to the three young detectives to solve the mystery.