As tales of a family holed up after an apocalypse go, “Shadows” isn’t particularly bad. Carlo Lavagna’s thriller has a decent sense of isolation and a time-tested source of conflict.

But the director of “Ariana” commits two cardinal sins in showing the lives of two teen girls and their all-knowing, self-sufficient mother. One is that is that where he’s taking us is laughably obvious. And the second is this obvious tale is so drawn-out as to give away the fact that he knows it’s stunningly predictable, but he figures that by padding out the story and the running time, he can fool the viewer and create a hint of suspense.

He can’t.

Mia Threapleton (Kate Winslet’s daughter) and Lola Petticrew are Alma and Alex, two teens who live in a room in the Stardust Hotel, not that long abandoned, but certainly going to seed. They keep each other entertained during the day in in a building whose windows are all covered over, sharing a room at one end of the place while Mom (Saskia Reeves) has her quarters at the other end.

“What’s the first rule?”

“Don’t go out during the day!”

Their lives are lived by lantern light, as their mother has told them of the dangers of daylight, of the perils of being out in it. She hunts and checks traps by night and keeps them fed. And they study the plants in the greenhouse, Mom’s school of nature, and other home school-able subjects.

All they know of the outside world they pick up from their mother, who has responded to whatever calamity has befallen civilization by going full naturism.

“Forgive us, Mother, for breaking the sacred bonds,” she prays to Mother Earth. “Thank you, Mother, for giving us everything.”

But young Alma is starting to have questions, and sister Alex is closing in on outright defiance. Mom goes off and leaves them on their own for days, and that fires their curiosity and creates opportunities for mischief. Going into the forbidden “cloak room,” where the detritus of “The Before” years are stored sets Mom off and pushes the girls towards open revolt.

So, Garden of Eden, Fall from Paradise parables anyone?

The acting is as effective as this simple script requires, with the odd animated or attempted emotional moment, most of which don’t land. As slow as it is, it feels as if there are details that’ve been left out, motivations under-motivated.

And it takes so long to get going that any delay in delivering us to the inevitable conclusion is downright interminable.

Rating: unrated, some violence, a sexual image

Cast: Mia Threapleton, Lola Petticrew and Saskia Reeves

Credits: Directed by Carlo Lavanga, scripted by Damiano Bruè, Fabio Mollo, Vanessa Picciarelli, Tiziana Triana A Red Water release.

Running time: 1:42