When Mary McDonnell took on a guest-starring role as Capt. Sharon Raydor on the fifth season of “The Closer,” no one could have anticipated that the “Battlestar Galactica” actress would be the one carrying the torch over from the TNT hit procedural to spinoff “Major Crimes.”

In rather serendipitous fashion, Kyra Sedgwick and McDonnell had run into each other at a party and expressed their mutual admiration and desire to work together. The result of their exchange quickly turned into an invitation for McDonnell to play Sedgwick’s nemesis in a guest arc.

“The scenes between Brenda and Raydor just sizzled with their conflict clash,” recalls exec producer Greer Shephard, who has been a writer on the show since its inception. “She made a very big impression. We all knew that there was an expiration date for Kyra, and I think that we were always trying to look forward and see how the show could carry on.”

In McDonnell, and a polarizing character whose trajectory very much resembled that of Brenda Leigh Johnson’s, they suddenly had their answer.

“Major Crimes,” which premieres next summer, is already a transition in progress. Some of the skein’s characters will be introduced throughout the latter half of the final season of “The Closer” and familiar faces will make a seamless move from one procedural to the other.

Whereas “The Closer” ended each episode with a confession, that’s where the story begins in the reboot, which ultimately focuses more on the justice system and its flaws.

The presence of the district attorney’s office will be introduced as part of the criminal process and the series will examine how confessions, which often given viewers closure in a case, sometimes aren’t enough to convict a defendant in court.

“You’re going to see how frail and human the justice system is,” says exec producer James Duff. “You’re going to see people struggling to create justice while dealing with their baser ambitions.”

Whether the show manages to live up to its predecessor depends largely on how invested fans are in McDonnell’s character and the crime-solving team they’ve come to know for the past seven years. It’s a gamble, but Entertainment Weekly TV critic Ken Tucker has no doubt they’re up for the challenge.

“The smart thing the producers have done is bring the supporting cast front and center in recent seasons, making them full co-stars with Sedgwick,” says Tucker. “Combine this with the way the show has woven Mary McDonnell into the show as Brenda’s nemesis and ‘Major Crimes’ is a model of how to make a franchise survive after its star departs.”

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