The Codebook Murders — Leslie Nagel

Amateur sleuth Charley Carpenter discovers a coded journal that could crack her small town's most infamous cold case wide open in this charming cozy mystery from the USA Today bestselling author of The Book Club Murders.
 
As the owner of Old Hat Vintage Fashions, Charley Carpenter supplies retro apparel to the residents of Oakwood, Ohio, but she's been known to set business aside to play detective when a mystery rears its head. And there's no bigger mystery in Oakwood than the murder of Regan Fletcher -- a case that's haunted the town for decades.
 
Regan's boyfriend, Carter, did time for the crime -- until another man's confession freed him. But did the “real killer” really do it? Or did Carter walk away with blood on his hands? When Charley stumbles on an old journal written in code, it only complicates the case by revealing a blackmail scheme that targeted dozens of Oakwood's citizens, giving them all a motive for murder. 
 
Now, with a spate of new suspects to pursue, plus a fresh murder and the abduction of her sleuthing partner, Charley must dig deeper still into the past -- even as she risks being buried by her shadowy prey. Joining forces with Detective Marcus Trenault and the newly formed Oakwood Mystery Book Club, Charley turns to a classic whodunit for clues on catching a killer -- before more lives are lost, and the truth dies with them.
 
Leslie Nagel's delightful Oakwood Mystery novels can be enjoyed together or separately:
THE BOOK CLUB MURDERS • THE ANTIQUE HOUSE MURDERS • THE ADVICE COLUMN MURDERS • THE CODEBOOK MURDERS