In order to keep people watching a TV drama series every week, it helps to have a loose plot thread — an overarching mystery that remains unexplained while the various story lines develop over time. The protagonist of the Friday night TBS serial, “Uta-Hime (Song Princess)” (10 p.m.), is Taro Shimanto (Tomoya Nagase), an employee of the Orion-za movie theater in a small Kochi Prefecture fishing town in the mid-1950s.

Taro was discovered lying unconscious on the beach at the end of World War II by the theater owner’s young daughter, Suzu. He was dressed in a pilot’s uniform and, when he regained consciousness, had no memory of who he was or how he got there. The theater owner essentially adopted Taro, making him the movie house’s factotum and a member of the family.

If this plot sounds familiar, then you probably saw the 2001 American movie “The Majestic,” starring Jim Carrey as a screenwriter who, in 1951, crashes his car in a California river and awakes with amnesia, after which he is taken in by the owner of a small town movie theater. “Uta-Hime” is based on a popular play of the same name that was first staged in 2004 by the Tokyo Seleccion Deluxe theater company. The company’s leader, Mikio Satake, wrote the play and adapted it for television, and, as far as I can tell, he has never acknowledged his script’s debt to “The Majestic,” which was an original screenplay.

But “Uta-Hime” and “The Majestic” differ in fundamental ways. As hackneyed as the amnesia device is, it works better in “Uta-Hime.” The main problem with “The Majestic” is that the theater owner believes the screenwriter is his son, a soldier who was missing in action in World War II, and the townsfolk incongruously end up believing he is the son, too. No such collective delusion afflicts the characters of “Uta-Hime,” who aren’t outwardly concerned about Taro’s background and quickly accept him as one of their own.

The most significant difference between the two stories, however, is the way they each exploit nostalgia. In both, the movie theater stands for a simpler time when people partook of entertainment as a community. In “The Majestic” those days are already fading, thus setting the stage for the advent of television, which is a private entertainment. The movie palace has closed down. The amnesiac screenwriter reopens it and in doing so revives the town, which had been depressed over the loss of so many of its sons in the war.

The nostalgia of “Uta-Hime” is strictly a function of marketing. The producers want to cash in on the current “Showa boom” and do so by dropping as many signifiers as they can into each weekly episode. Every week there’s a meal that features some emblematic 1950s dish, like “rice curry” (as opposed to today’s “curry rice”), and popular products of the era, like Lotte Green Gum and three-wheeled motorcars, are positioned prominently.

Still, the producers also seem to be aiming the series at a demographic that doesn’t have any nostalgic feelings for the era depicted since it’s members weren’t even born yet. The most important consideration for a commercial TV drama is its cast, and this one contains the usual mix of young idols and topical comedians, though it also includes a few of the actors who appeared in the original stage play. Some 1950s melodies are used as incidental music, but the theme song, “Seishun,” was written by 1980s (late Showa, as it were) rock god Tsuyoshi Nagabuchi and performed by boy band TOKIO, of which Nagase is the lead singer. Then there is the totally gratuitous inclusion of Eric Clapton’s 1996 hit “Change the World” anytime the story calls for a wistful mood.

As with most TV dramas, the production design is better than the writing or the acting. Re-creating the look and sound of a Showa Period (1926-89) small town requires close attention to detail. It’s mainly a technical challenge. However, nobody watches a TV series solely for its production design, which brings us back to that loose plot thread. Halfway through the series, the subject of Taro’s past is finally brought up with the arrival in town of a woman from Tokyo who speaks with a strong Tohoku accent. She seems to have some connection to Taro’s past and is complicating the budding romance between the amnesiac and Suzu, who has grown into a young woman with a huge crush on the big, dumb lug.

But that’s not the only loose thread. Basically, the entire series is one long flashback told through the experience of a hapless young man (Nagase again) whose mother, a famous Showa Period pop singer, has ordered him to visit the Kochi town where she grew up and whose one movie theater, the Orion-za, is about to close down. He goes there and learns that the last screening will be of the Showa Period movie “Uta-Hime,” which the late owner requested be shown when the theater shut its doors for good.

The implication is that the story we are watching is the “real life” basis of the story depicted in that film, and there are plenty of clever clues that, taken together, start to explain why the singer insisted her son see the movie, which has something to do with his grandfather. The movie’s screenwriter, for instance, is named James Taro, and one of the characters in the flashback is a student who affects the look and attitude of James Dean, whose “Rebel Without a Cause” played at the Orion-za. Is he James Taro? Or is Taro James Taro?

There are many problems with the script, the most glaring one being that much of the story is advanced by means of overheard conversations, a plot device as trite as amnesia. But some of the most popular TV series have had worse writing, so something else has to explain why “Uta-Hime” has earned the lowest ratings of all the fall drama series. Perhaps people’s memories of Showa aren’t as fond as the media think they are. Or maybe Nagase isn’t such a big draw. Or maybe the loose plot threads that demand the viewer stick with the series until the end are a little too loose. Or maybe, like me, everyone is already sick of that Eric Clapton song.