Michael Connelly has kept a freshness to each of his novels about LAPD Detective Harry Bosch by discovering new aspects about his perennial hero, and by bringing in solid, believable characters to inhabit Harry's world.

His mission to ferret out criminals has never gone smoothly for Harry, and Connelly's decision to age Harry in each novel has brought challenges. In 2017's "The Late Show," Connelly introduced LAPD Detective Renée Ballard, an insightful and tenacious investigator relegated to the midnight shift, or the "late show."

Now in "The Night Fire," Renée isn't just a supporting character, she's a full-fledged partner of Harry — albeit off the books — as shown by the subtitle "A Renée Ballard and Harry Bosch Novel."

It's telling that Harry gets second billing but he certainly isn't in the background of "The Night Fire." Renée isn't some wide-eyed innocent who needs a mentor; she's an experienced detective, equal to keeping up with Harry. She and Harry share a similar skill set yet their differences make for good tension and a plot that again showcases Connelly's high standards.

"The Night Fire" finds Harry feeling his age. Nearly 70, he's using a cane as he recovers from knee surgery and he has another health scare. But Harry still has "that fire" to solve cases — no matter how many years ago the crimes occurred — and he knows that Renée does, too.

Harry's recently deceased mentor, Detective John Jack Thompson, left instructions to his widow to give Harry the murder book files for the unsolved killing of ex-con John Hilton, shot to death in his car while parked in an alley nearly 20 years ago. Harry wants to honor the memory of Thompson, who was often a substitute father to him, though he is curious why his mentor took the case files but never investigated the murder. Retired from the LAPD and his role as a volunteer working cold cases for the San Fernando police department tenuous, Harry needs someone with a badge — and the resources — to help him work the investigation. That would be Renée.

As Renée and Harry team up to solve the Hilton case, they each work separately on other cases. Renée delves into the arson death of a homeless man while Harry looks at the case of a man being defended by his half-brother, Mickey Haller, accused of killing a Supreme Court judge.

Breathless action and deep character studies enhance "The Night Fire" as the story alternates between Harry's and Renee's point of view. "The Night Fire" is Connelly's 21st outing with Harry, but the author has so much more to show us about him. Only three books in, Renée has even more fodder for Connelly to uncover.

In "The Night Fire," Connelly again shows his mission — strong plots and sturdy characters.

Oline Cogdill is a member of the National Book Critics Circle.