Mystery of the Man in the Mirror

A brother and sister, 10 and 13 years old, are recruited by a mysterious man, trapped in a mirror, to travel back in time to the year 1939 and clear him of a crime he did not commit. To do this, they masquerade as adult detectives and roam Los Angeles, questing gangsters, and their molls as they seek to find the true murderer.

Jake and his younger sister, Darlene, while temporarily staying in a downtown residence in Los Angeles, come across a skeleton key to a door that strangely no one else in the building can see. Printed on the frosted glass of the door is the name, Archer Wolfe, Private Detective. As they enter, they find two rooms furnished with strange furniture dating back to the 1930s. Exploring further, they discover the ghost of Archer Wolfe trapped in a mirror on the wall. Convicted and executed for a murder he did not commit, the detective has one request for Jake and Darlene and that is to venture through 1930s Los Angeles as private detectives and find the real murderer so he can be exonerated of the crime. However, they must accomplish this within a short amount of time because the ghost of the detective and his world of the 1930s will soon vanish.
Mystery of the Man in the Mirror fits as a children's book, a young adult fiction book, and falls into the mystery adult noir genre as well.