"Unaccountable" wraps up the Abby Series, and presents retired New York Police Detective Carl Boone in his own right, while introducing Marianne Bell. Together, Boone and Bell form the basis for the Boone-Bell series. Life for Abby and her husband Russell has returned to normal. Now in her first trimester, Abby is called on to sort out the estate of an elderly client, a retired FBI agent. Meanwhile, the fiancée of 'Toph' Lefan, Russell's murdered friend, is seeking answers. Russell refers her to former New York State Police Detective Sergeant, Carl Boone, who has just opened his own office as a private investigator. Knowing the power and far-reaching influence of those indirectly responsible for Toph's murder, both Russell and Boone try to dissuade her, to no avail. No one could have foreseen how Abby's work on the estate, and the fiancée's quest for information, would trigger individuals within the FBI into raising a wall of silence around evidence suspected to be in the deceased agent's possession, evidence they would do anything to hide.