Bestseller Brennan's intriguing sequel to 2020's The Third to Die takes Matt Costa, the head of the FBI's D.C.-based mobile response team, and his team, including Kara Quinn, an LAPD detective on permanent loan to the MRT, to Tucson, Ariz., to investigate two potentially connected cases: the murder of an environmental activist college student and the possible illegal dumping of toxic waste by a nearby copper refinery. The refinery owner's son provides assistance by becoming an informant for Matt. Meanwhile, Kara goes undercover as a bartender at a hangout for refinery workers, and her colleague Michael Harris, a former Navy SEAL, takes a job at the refinery. More deaths occur, and the team gets on the trail of a vicious criminal gang. Amid the fast-paced action, Matt, Kara, and Michael each take time to ruminate on their dysfunctional love lives. These bumps in the narrative may frustrate readers eager to get on with unraveling the well-constructed mystery plot. Fans of romantic thrillers will best appreciate this one. Agent: Dan Conaway, Writers House. (Mar.)

In rural Arizona, Special Agent Matt Costa commands the FBI Mobile Response Team's investigation into the murder of an environmental-science intern who was attacked while collecting evidence of illegal toxic-waste dumping. Lacking physical evidence, the case is going nowhere until Joe Molina, heir to the Southwest Copper refinery, agrees to inform on David Hargrove, the executive responsible for the illegal dumping. With key information coming in from undercover officers Michael Harris and Kara Quinn, and the team's forensic accountant digging into Hargrove's sideline trucking business, the team is closing in quickly. But the game changes when Hargrove is murdered and another body turns up, along with evidence of human trafficking. Costa knows his team's safety relies on finding the connection between the murders, the trafficking, and the illegal-dumping scheme. Brennan showcases a range of fascinating procedural detail, from undercover ops to forensic accounting, in this sequel to The Third to Die (2020). Pair this series with J. A. Jance's similarly team-driven Ali Reynolds thrillers.