Dr. Troy (Julian McMahon, left) and Dr. McNamara (Dylan Walsh) return to business tonight on nip/tuck.

PRASHANT GUPTA

Julian McMahon plays Dr. Christian Troy on nip/tuck, which returns for its fourth season tonight at 10 on cable TV’s FX.

PRASHANT GUPTA

Tonight nip/tuck,the lurid, over-the-top tale of two plastic surgeons in sun-drenched Miami, returns to cable TV’s FX at 10 to begin its fourth season, and it doesn’t take long for things to get twisted. There’s plenty of help from well-known guest stars, too, among them Larry Hagman, Rosie O’Donnell, Brooke Shields and Richard Chamberlain.

When we left nip/tuck at the end of the show’s third season, viewers finally discovered the identity of The Carver, a knife-wielding slasher who was waging a personal war against the standards of human perfection that Dr. Troy and Dr. McNamara made a very good living upholding.

In an ending that some found both improbable and contrived, The Carver turned out to be a brother-and-sister team. In a recent phone interview, Julian McMahon, the Australian actor who plays Dr. Christian Troy, said he wasn’t a big fan of the entire season.

“It wasn’t my favorite period of the show, I’ll just leave it at that,” he said. “But I’m very happy about this season. I think it’s my favorite one so far.”

We start the new season with the two doctors ready to commemorate their 5,000th surgery together. The show portrays Dr. McNamara (Dylan Walsh) and Dr. Troy as polar opposites. McNamara is the devoted family man who yearns to do good. Troy is the handsome, vain, sexual athlete who yearns to make money and chase women.

Of course, once nip/tuck establishes the parameters, it immediately starts toying with them, as McNamara’s good intentions continually lead him into rotten choices, particularly regarding his family. The show’s basic premise has always been the contrast between the physical perfection Drs. Troy and McNamara are selling and the mess they are making of their lives.

“We know as soon as we do something definitive, it will end badly,” McMahon said.

In tonight’s episode, Dr. McNamara, reunited with his now-pregnant wife Julia (Joely Richardson) leaves a bar early to be with his spouse. Dr. Troy, also thinking of family, leaves for a sexual romp with a mother-and-daughter duo.

“It’s a great way to get back on track,” McMahon said. “Let’s establish the original dynamic, and then (mess) with it.”

Of course, it never takes long for nip/tuck to get strange.

The surgery is gory, the sex and language are as explicit as basic cable allows, and the plots can get downright bizarre.

Certain patients stick in the memory, among them an ape, a male journalist who wants breast implants so he can empathize with his wife who has breast cancer, and “Mama Boone,” a hugely obese woman whose flesh actually grew into the fibers of her couch. It wasn’t pretty.

Small wonder that organizations such as the Parents Television Council (PTC) can’t stand nip/tuck.

“Actually, I think they have a point,” McMahon said. “There are certain age groups that shouldn’t be watching. But we put a massive amount of disclaimers on the screen before every show. We’re not just throwing it out there.”

Many plastic surgeons weren’t fans, either, he added. At least, not at first.

“There was a big uproar at first that we were doing everything wrong. . . I think now everyone realizes that it’s a TV show. We’re trying to create something dramatic, not demonstrate surgery.”

And McMahon said nip/tuck is intended to be taken with a grain of salt.

“There’s a wink between us and the audience,” he said. “We know we’re a little ridiculous, a little over the top. Let’s all be in on the joke.”

Certainly the show’s guest stars seem to be enjoying themselves, often poking fun at their own images.

Larry Hagman plays a business executive who wants some cosmetic surgery of an intimate nature. He’s so pleased with the results that he buys the McNamara/Troy practice, and installs his beautiful young wife (Sanaa Lathan) to watch over his business interests. It doesn’t take a psychic to see complications looming on the horizon.

Kathleen Turner plays Cindy Plumb, who wants a “voice lift” so she can continue her career as a phone-sex goddess.

Richard Chamberlain stars as gay sugar daddy Arthur Stiles, who’d like his much younger boyfriend to reflect his own image. “We can’t all be born with these cheekbones,” Chamberlain says proudly, tilting back his head to catch the light.

Other guest stars this season include Peter Dinklage, Catherine Deneuve (who wants her late husband’s ashes put in her breast implants), Brooke Shields and Rosie O’Donnell. O’Donnell is an interesting choice, since in her public statements she has not exactly been a fan of plastic surgery.

McMahon said he didn’t want to give away the entire O’Donnell storyline, but he said she portrays a housewife who wins a huge lottery, and decides some big changes are in order for her and her family. “It’s absolutely hysterical,” McMahon said.

McMahon got his start on Australian TV, then broke into American TV on the soap opera Another World. Other TV credits before nip/tuck include Profiler and Charmed. On the big screen, McMahon played the evil Dr. Doom in Fantastic Four and recently finished Premonition, with Sandra Bullock.

His father, William McMahon, was prime minister of Australia from 1971 to 1972. But Julian McMahon said the level of attention was nothing like what it would have been for, say, the son of an American president. “Fame in Australia is very different from fame in the United States,” said McMahon, who now lives in Los Angeles.