It is 2001 and the police constable's girlfriend is murdered in a fit of jealous rage. When the constable realizes what he has done, he manages an elaborate cover-up. Only one person knows the truth.
Flash forward to 2012. Anne Brown is still running her late uncle, Bill Darby's, detective agency after spending four or five years as his assistant. One day, the postman delivers an eleven year-old letter. The letter is addressed to her uncle from a woman named Carolyn Jollimore. She says she has evidence about a murder and begs for help from Darby. But Bill Darby is dead. And when Anne looks up the letter's author, she finds that Jollimore too is now dead. Troubled with the evidence at hand, Anne must decide if she should investigate this eleven-year old murder.