(CNN) -- The "Law & Order" television franchise is well-known for its turnover -- and its seemingly fearless willingness to replace characters beloved by fans.
But when "Law & Order: Criminal Intent" returns Tuesday night for its ninth season, it will be testing that formula -- and viewers' tolerance for change -- even further by replacing almost the entire cast of main characters.
The dearly departing include actors Vincent D'Onofrio, who portrayed Det. Bobby Goren; Kathryn Erbe, who played his partner Alexandra Eames; and Eric Bogosian, who is leaving his role as Capt. Danny Ross.
Only Jeff Goldblum, who came on board last season as Det. Zach Nichols, is returning. He will be joined by new cast members Saffron Burrows as Nichols' new partner, Serena Stevens, and Mary Elizabeth Mastrantonio as Capt. Zoe Callas. Julianne Nicholson, who played Goldblum's partner, has also left the show.
"From a business perspective, I think it makes sense," said Al Norton, a columnist behind the Two Tivos To Paradise blog and a writer for 411mania.com. "The show probably wasn't going to pick up many new viewers and it allows you to debut almost a brand-new show. But you also run the risk of alienating your core fan base."
Though ratings have never been astronomical -- it frequently finished fourth in its time slot while it was on network television and in 2009 it ranked as the number three drama on basic cable among viewers 18 to 49 -- the show has a strong core of fans. They rallied when news broke that the series might be canceled by NBC after its sixth season, which prompted the unusual step of moving the original episodes to the USA Network, where reruns had performed well.
Many of those same fans are now in a tizzy ahead of the planned two-part special that reportedly wraps up the Goren and Eames storyline and includes the death of a character.
"There are a lot of fans out there that are extremely upset about it because Vincent and Kathryn have been with the show from the beginning," said Christine Zimmer, who runs the blog All Things Law & Order. "I think a lot of them are feeling betrayed."
Walon Green, "Criminal Intent's" showrunner, said fan reaction is tough to predict.
"We certainly made an effort with the first show to [allow] people who were huge fans of Vincent and [Kathryn] see them go out with a couple of good episodes and in a dignified fashion," he said. "And also to bring in Jeff and Saffron in a way that seems legitimate that the baton would be passed to them."
Green added that "Criminal Intent" has been able to carve a unique niche among the many police procedurals on TV.
"It isn't so much who did it and how they did it, it's why they did it," Green said. "It gives you a lot more leeway to explore the psychology of these people who do these things which so effect our consciousness and sensibilities."
"L&O: CI," as fans refer to it, is one of three in the franchise, which includes the original "Law & Order" and "Law & Order: Special Victims Unit." The show follows the "ripped from the headlines" approach of the original, with the crimes being investigated by the New York Police Department's Major Case Squad.
Perhaps the biggest reason for the show's success is the unpredictable D'Onofrio (best known for playing Pvt. Pyle in "Full Metal Jacket" and the bug-infested Edgar in "Men in Black"), whose tics and delivery have made him nothing if not interesting to watch. George Yang, who heads up a "Criminal Intent" fan group on Facebook, said the new cast will test the strength of the series' fan base.
"So many people are major fans of Vincent [D'Onofrio] and he's been a really big draw for the show," Yang said. "With him gone, it's going to be interesting to see if people still want to watch."
Zimmer said that, for her part, she has enjoyed Goldblum's character. The unknown at the moment is how well he will mesh with the new actors, she said.
"His character, I think, has just the right amount of oddities about him that made viewers want to learn more about him," she said. "The litmus test will be with Saffron and how she comes in as to whether fans will accept all this change."
Writer Norton said the risk to shake things up a bit might pay off for the series. He said he was able to view an advance screener of the new season's premiere episodes, and he predicted that hardcore fans will not be thrilled with the exit of D'Onofrio and Erbe's characters.
"I don't think it does justice to the characters and the work that D'Onofrio and Erbe have done," Norton said. "Certainly there is a high body count and a finality to it, but for the fans that have invested so heavily in the characters and this show, I don't think they are going to be satisfied."