Allison Osborne 
Circle Code Conundrum [PDF ebook] 

With two weeks in a new home, and a solved murder, under their belt, Irene and Joe are eager for another mystery. When Eddy brings them a curious case involving a jumbled circular message, they jump in with both feet. But as they attempt to crack the cipher, they uncover a dark past of a seemingly innocent young woman and a cover-up that may put them both in grave danger.