A modern-day 13-year-old boy and his 10-year-old sister travel back in time to the year 1939 in an attempt to exonerate a private detective wrongly accused of murder.  

Temporarily staying in a building built in 1918 in downtown Los Angeles, the kids discover a skeleton key that opens the door to the offices of a long dead private detective. Entering, they step back in time to 1939, the year the private detective was executed. In an inner office, they come upon the ghost of the detective trapped in a mirror on the wall. With only two weeks before his presence disappears from the mirror, the detective pleads with the kids to uncover the real murderer and exonerate him of the crime.  

Taking up the challenge, the kids are hampered by the time constraint, combing for evidence through the unfamiliar bygone days of 1939 Los Angeles and confronting the motley crew of mobsters and molls who inhabit it. However, the kids are helped by the fact they are not recognized as children but as adults. Dressed in the fashions of 1939, and using the skeleton key to open doors to the past throughout Los Angeles, the kids venture out, successfully passing themselves off as gruff 1930s private detectives. 

With its period slang and references, this novel is an homage to noir detective mysteries of the 1930s and a literary feast for fans of hard-boiled fiction, such as that of Hammett and Chandler. Also, listeners who are familiar with the history of Los Angeles will appreciate the shout outs to Coles, the Fred Harvey House at Union Station, the Aztec Hotel on Route 66, and other local landmarks.