Books like Acts of mercy by Mariah Stewart

When rookie prosecutor Jessica Hughes crosses the son of a major crime boss, she's determined to bring him to justice--if his family doesn't kill her first. And with newly minted FBI special agent Zach Taylor protecting her, she believes she can succeed. Zach will do anything to stay ahead of the crime syndicate and guard Jessica while she builds her case. The more time he spends with her, the more personal the assignment becomes. It's bad timing for falling in love, but as the threats against her life escalate, Zach realizes Jessica is everything to him--and he will do everything he can to make sure she has a future.

A police detective and a federal agent who meet on the job are drawn to each other on the personal level, and the story unfolds as they both start to uncover the secrets of Ann Silver's life.

After Nolan, a California beat cop, adopts the daughter of a notorious drug dealer, the ruthless father vows to take back his only child. In response, Ann flees across the country, changes her name, and starts a new life as an investigator for the Mercy Street Foundation, the billionaire-endowed organization dedicated to finding missing persons. As Emme Caldwell, she takes the lead on the Foundation's first case: Nineteen-year-old Belinda Hudson disappeared from her sorority house leaving behind only one cryptic clue. Retracing the vanished student's steps leads Emme to Heaven's Gate, a fertility clinic, ad the mysterious Donor 1735. Belinda's legal guardian, Nick Perone, is determined to shadow Emme's every move as she searches for his niece. But the closer Emme gets to Donor 1735 and the chilling truth, the more apparent it becomes that she's escaped one dangerous man only to run head-on into another--one who's far more determined and every bit as deadly.

A former FBI agent seeks to exonerate her father and uncover the truth behind a decades-old murder of a prostitute, spurring a new investigation that threatens to reshape a community.

Forensic pathologist Kyra Elliott must solve a serial murder case using skeletal remains, partnered with former friend and FBI investigator Joshua Richards—his reluctance turns to trust as they close in on the killer and each other.

FBI agent Mia Shields teams up with Chief Gabriel Beck to stop a serial killer who cages victims in plastic, leaving recorded last words as chilling clues.

A former FBI trainee, Miranda Moore, survives a serial killer and now hunts his latest victim, a Montana college student, as the FBI interrupts her relentless pursuit of vengeance.

Chicago detective J. T. Logan, now a small‑town sheriff, must save his kidnapped daughter while FBI agent Madison Spencer joins the hunt, turning a crime‑scene into a tense, romance‑laced pursuit.

An FBI agent with an autistic brother hunts twin psychics who kidnap children for a madman's sinister experiments, racing to save the most vulnerable before they vanish into darkness.