In this intricately rendered psychological tale, part murder-mystery and part exploration of a sibling relationship, Ellie Enderlin works as a successful international coffee buyer in San Francisco. Over the years, Ellie’s life has been full of troubles and dissatisfactions, most notably the unresolved death of her younger sister, Lila, who was brutally murdered in the winter of 1989.

A numerical prodigy who was studying for her Ph.D. at Stanford University, Lila was set to revolutionize the field of mathematics in a world where she formed relationships with certain numbers in the same way avid readers develop relationships with characters in books. But when Lila’s body was discovered in Armstrong Woods, a remote area just north of San Francisco, all the hopes and dreams that her parents had for her vanished.

The years pass. Lila’s murderer is never discovered, and Ellie gets on with her life, trapped in her own state of imaginary numbers, her detachment from the events of the past providing a peacefulness and a safety she knows she needs. Part of Ellie’s remoteness has to do with the endless conversations she had with Andrew Thorpe, her ambitious English professor, who despite Ellie’s protestations, went ahead and published a nonfiction account of Lila’s life leading up to her death.

The book, called Murder By The Bay, a work in the same vein as In Cold Blood, detailed Lila’s family life and ended up becoming a national bestseller and rocketing Thorpe to literary stardom. Ellie and her parents, however, were devastated by the fact that their private heartache was made so public. Even more sensational is that Thorpe claimed the police had not given a detailed hypothesis of Lila’s killer and that the evidence pointed to Peter McConnell, a married fellow Stanford graduate who was having an affair with Lila in months leading up to her murder.

Although much of the evidence condemning Peter was circumstantial at best, based mainly on lurid supposition, he was tried in the court of public opinion. With his career and marriage over, Peter was forced to flee, hiding out in a small village in Nicaragua, where Ellie, on a coffee-buying expedition, inexplicably reconnects runs with him at a local café.

From the moment Ellie begins talking to Peter, she finds it hard to believe that he’s a heartless and calculated killer. Struck by the softness of his eyes and the gentleness of his voice, for the first time she realizes that Thorpe’s book has deeply influenced the way she constructed her story. At the time, she was young enough to believe that the things Thorpe said about Lila’s murder were true. Now she realizes that something is terribly wrong with her interpretation of the events from all those years ago.

The weight of Ellie’s guilt and grief propels Michelle Richmond’s devastatingly beautiful story forward. Like one of Lila’s complicated mathematical equations, Ellie tries to place the pieces of the puzzle together. Peter was the obvious choice all along, the most likely suspect, but as she reflects on her own relationship with Lila, she begins to doubt that Peter could have been the one who so viciously brought a stone down upon Lila’s head, as Thorpe had theorized.

Making the most of San Francisco and its surrounds - Candlestick Park, the Mission district, Castro Street, and the Folsom Street fair - the author exquisitely interlocks Lila’s mathematical formulae with Ellie’s memories of her sister, even as she can’t quite banish the thought that she’s still living a life as an “imaginary number.”

As Ellie works hard to deconstruct the mystery surrounding Lila’s final days, every fact and supposition of Thorpe’s story begins to fall like a fragile house of cards, and she realizes that she’s been blindsided by the sense of mythology that has surrounded Peter McConnell. She has believed far too long in his guilt to simply let that conviction slip away, and her grief has blinded her to logic.

The mathematical equations add a unique element to the narrative, but most compelling are the author’s insights into the nature of storytelling along with the complex moral and emotional aspects of losing a loved one, especially under such horrendous circumstances. In the end, the capturing of Ellie’s essential spirit as well as that of Lily’s genius make this story so compelling as Ellie’s discoveries gradually unfold, shifting forever her perceptions of her sister and of the world as she knows it.