WE WERE KILLERS ONCE is the fourth installment in Becky Masterman's mystery series featuring retired FBI agent Brigid Quinn. Following a career as a profiler for the Bureau and some philosophical difficulties with her supervisors, Quinn is now a private investigator in Tucson, Arizona. That city becomes an enjoyable venue for Masterman’s novels as it combines elements of the Old West and frontier with the modern qualities of a community that is home to the University of Arizona and a multi-ethnic population.

In the first three books, Quinn is a typical private detective whose only remarkable trait is how tough she is for a woman eligible to receive Medicare benefits. But this fourth entry is far different (in a good way), offering readers a page-turning and gripping story. In the previous novels, Quinn’s husband Carlo, a former priest and university professor, was a minor character. His appearances often involved sharing a glass of wine or having dinner with his wife as she discussed the case she was working on. These stories often focused more on what information Quinn was withholding from Carlo than what she was telling him about her work.

"Carlo’s involvement in the plot makes WE WERE KILLERS ONCE the best entry in the series, as it provides readers with far more information about his life, as well as the life he shares with his wife."

But in WE WERE KILLERS ONCE, Carlo is an integral part of the plot in his own right. In fact, he is the engine that runs the novel. Unknowingly, Carlo has become the target for a man on the run from his past who believes that Carlo is the final roadblock preventing him from living out his years without the threat of returning to prison. Jerry Beaufort had been sentenced to life imprisonment as a “three-time” offender. The harsh three-time loser laws were a leftover from the tough-on-crime 1970s when prisons were constructed at a rapid rate and laws were passed to fill them. But recent years have seen a downturn in crime, as well as a desire by state officials to spend funds in other endeavors rather than incarceration. After serving 33 years, four months and five days of a life sentence, state officials decided to release Beaufort. After all, he was not a violent criminal; he was only a drug dealer.

But Beaufort has a secret past, and it is his life from decades ago that makes WE WERE KILLERS ONCE such an enjoyable mystery. Using the true story made famous by writer Truman Capote in his book, IN COLD BLOOD, Masterman has created an alternative tale that weaves Beaufort into the 1959 account of the Clutter family, murdered in Holcomb, Kansas, by Perry Smith and Dick Hickock, who were apprehended after a national manhunt, convicted and executed. Added to the plot is a similar crime committed in Florida two months after the Clutter murders. In Sarasota, Florida, four members of the Walker family --- Christine, Cliff and their two children --- were killed in their home. That crime is still unsolved, although in 2012, new information came to light linking Smith and Hickok as the potential culprits. The two men had actually been suspects as far back as 1960.

Masterman weaves these two events into an enthralling story by adding the possibility of a third man, Beaufort, into the criminal equation. Before his execution, Hickok sought to confess his sins to a Catholic priest in the Kansas prison where he was incarcerated on death row. Beaufort believes that the confession could send him back to prison and that eliminating anyone with knowledge of the details will keep him a free man. He has everything figured out, except for the fact that the priest is now married and his wife worked for the FBI.

Carlo’s involvement in the plot makes WE WERE KILLERS ONCE the best entry in the series, as it provides readers with far more information about his life, as well as the life he shares with his wife. All of this humanizes Brigid Quinn in ways more entertaining than in the previous novels. Seeing the human side of our protagonist makes her a far more compelling character, and it will be interesting to see where Masterman takes her in future installments.