The scariest part of “The Ring Two” is not the derivative plot, or the nonsensical ending, but the frighteningly complete degeneration of Rachel Keller’s (Naomi Watts) believability as a character. In the first “Ring,” she was a crackerjack journalist, a smart investigator and a loving mother. Flash to the sequel and we find a scatterbrained, stereotypically brainless blond, possessing the body but definitely not the soul of the original. The film as a whole suffers a similar fate in the bumbling hands of director Hideo Nakata (who directed “Ringu,” the Japanese film on which the first “Ring” was based). Nakata doesn’t have the knack for the unsettling visuals that his predecessor Gore Verbinski (“The Ring,” “Pirates of the Caribbean”) conjured from the cold Pacific Northwest landscape.

The movie’s screenplay disappoints at every turn. Once through the standard kill-an-attractive-teen opening, the story picks up with Rachel, who has moved to Seattle with her son Aidan (David Dorfman) to start a new life. But she can’t escape Samara, the barnacle encrusted devil child (Kelly Stables and archive footage of Daveigh Chase, the original). Samara possesses poor Aidan on the night of a sickle moon — a reccurring image that is supposed to symbolize a partially open well, but instead looks suspiciously like the Dreamworks logo.

Rachel becomes worried as pictures of Aidan begin to show Samara in the background, and a gigantic tree of fire grows in his bedroom. She cannot help but put the symptoms together to diagnose Aidan with hypothermia, of course. By the time he morphs into the devil child, Rachel realizes that something more serious is going on and sets ditzily out to find a cure for her son.

The plot proceeds linearly from there, but for a more complete synopsis think a combination of the 1956 classic, “The Bad Seed,” “The Exorcist,” and “Nightmare on Elm Street,” only without the humor or genuine horror. Yet “The Ring Two” can’t even muster enough imagination to join these stolen plot elements together. The whole production behaves like a bad sketch comedy show, with isolated horror vignettes deadened by pointless filler in between.

Nakata’s sense of what’s scary is also oddly out of joint. In the film’s strangest scene, a pack of wild deer attack Rachel and Aidan in their car. Not the least bit frightening, this reversed hit-and-run inevitably gets howls from the audience. (Nakata would have done better to just repeat the crazed horse attack in “The Ring.”) Other scares, while not as ridiculous, consistently fail to frighten — the supposed climaxes hardly ever match the nail-biting, screeching score.

It doesn’t help that Dorfman is utterly unconvincing as Samara-in-Aidan, delivering all his lines with a monotone that grates the nerves. His makeup is little better, lending him the unsavory complexion of a dead fish. Luckily, Sissy Spacek makes a surprise appearance as Samara’s insane mother, prophesizing death while eyeing Rachel with an eerily glowing face peeking out beneath tangled black hair. After all, Spacek, the star of Brian De Palma’s “Carrie,” knows a thing or two about horror films.

Other than Spacek, Watts is the only one who actually tries to act. Despite ill treatment from the inane script, she emotes like mad, struggling to stretch a role out of a microbe-sized character. But in scenes like the deer attack, even her well-groomed talent escapes her, and she throws in the towel with a confused expression.

Working against his actors, Nakata seems to systematically turn the major strengths of “The Ring” into liabilities. He destroys the first film’s intricately crafted suspense to the point that it becomes almost a farce, proceeding to the major scares with way too much build-up. Every action, from putting a tape in a VCR to walking down stairs, is done so slowly and deliberately that one feels the filmmakers desperately trying to wring every last drop of fright from the story. Nakata also dwells on the famously elongated death faces for too long; when examined closely, they just look silly. He just doesn’t hit his stride until a seriously scary scene in a well near the end, but by then he has lost the last scraps of honesty, the backbone of every horror movie.

Samara represents warped fears felt by many parents, those of killing their child and being killed by their child. The trick is to tap into that reality, which “The Ring” did. Nakata settles for a glossy, safe Hollywood fantasy that takes itself too seriously to be a fun spoof. Hopefully this well will stay closed for good.