Melodrama derailed by cosmic debris

Streaming has been a blessing and a curse for storytellers. Just because something can stretch out to eight hourlong episodes doesn’t mean it should.

Amazon Prime’s “Night Sky” stars two Oscar winners, Sissy Spacek and J.K. Simmons, as Irene and Franklin York, a couple aging in place in a bucolic small town. Irene has not quite recovered from an unspecified accident, and their conversations allude to the loss of a son. Franklin shows signs of forgetfulness that might indicate deeper issues.

Irene’s problems are less obvious, but they trouble her deeply. When she visits a recently widowed friend at a senior facility, we’re shown how aging and memory loss cut both ways. Irene fails to recognize a former prized student, and Irene is in turn forgotten by her grieving friend, a woman who can’t utter three sentences without forgetting the first.

Such scenes show us how good and how powerful “Night Sky” might be if it were a simple movie-length meditation on love, aging and loss. Instead, Irene and Franklin’s story is tethered to a science-fiction conceit that straddles the fine line between magical realism and just plain ridiculous.

For, in addition to the accumulation of decades, their dusty backyard garage contains a cosmic secret. Beneath its floorboards is a portal to another planet, light-years away. In their own humble ways, Irene and Franklin treat it like an intergalactic sunporch, retreating to their hole in the ground to stare at the alien landscape and distant moons, planets and constellations. Their plaid recliners lend a homey touch to their observation deck.

Is this a delusion? A metaphor? Or a portal to an extended and distracted story? Sadly, it’s the latter. Irene and Franklin may survive their trips into outer space, but “Night Sky” can’t withstand the radical shift in tone and emphasis. One minute, it seems like an old Horton Foote drama, and the next, it’s “Jessica Tandy and Hume Cronyn on Mars.”

“Night Sky” is not the first series to borrow story

and tone from the old “Twilight Zone” series, while forgetting that Rod Serling’s best tales unfolded in half-hour dollops. “Night Sky” loses focus by the end of the first hour. You might require some kind of underground portal to make it to the eighth episode.

If Spacek’s performance seems a little familiar, it’s because the “Carrie” star returned to the Stephen King universe in the first season of Hulu’s “Castle Rock” as a woman addled by dementia. She’s also

no stranger to basement bunkers, having spent 30 years in a bomb shelter with Brendan Fraser and Christopher Walken in the great 1999 comedy “Blast From the Past.”

› Other streaming debuts include the show business satire “The Valet” (Hulu), starring Eugenio Derbez as a parking attendant who is enlisted to pose as a movie star’s boyfriend to get her out of a public-relations disaster.