It should have been a routine investigation. Instead, DEA K-9 agent Adam "Deck" Decker watches in horror as one Denver hospital seems to be ground zero for overdoses of a new drug. Now Deck can only hope a certain ER doctor will help him and his canine partner track down the source. Dr. Tori Sampson has her reasons for not trusting federal agents, especially ones working for the DEA. But the rash of overdoses—including a heartbreaking case involving a teen—is alarmingly high. And the new opioid is not only extremely dangerous, it defies all the usual medical treatments.

Crack CIA analyst Trista Gold is a whiz with the computer, but not so much with people. She hides behind her job, analyzing top-secret code and making recommendations on national security. CIA K-9 officer Sgt. Matt Connors suspects that beneath Trista's uptight appearance, there's a sexy woman itching to cut loose. But he doesn't dare act on his attraction. He's a loner and always will be. Keeping away from Trista is a must-do directive. Until he doesn't have a choice. During a routine assignment, Trista stumbles across a cryptic exchange. Then someone tries to murder her - twice.

Meg and Hawk are part of the FBI's elite K-9 unit. Hawk can sniff out bodies anywhere - living or dead - whether it's tracking a criminal or finding a missing person. When a bomb rips apart a government building on the National Mall in Washington, D.C., it takes all of the team's extensive search-and-rescue training to locate and save the workers and visitors buried beneath the rubble.

Private investigator Kenna Banbury lost everything two years ago at the hands of a serial killer. From the ashes of that encounter, she’s built a life she believes in, searching for the lost and forgotten all over the western US. When a series of murders drags her into an FBI investigation, Kenna finds herself back in the place where it all went wrong. Struggling to make sense of the case, Kenna’s past and present collide in a deadly plot that risks another betrayal and threatens to shatter everything she’s built.

As a former smokejumper, arson investigator Bri Tucker knows her way around fires. But after a mysterious blaze takes the life of a former colleague, Bri inherits a curious puzzle from him that raises questions about several fiery deaths. Someone, however, doesn’t want her picking up where he left off in search of answers. When she teams up with ATF Special Agent Marc Davis to solve the puzzle, the case heats up—as does the attraction between them.