“Eat drink and be merry, for tomorrow we may die”—a notion as ancient as the Bible itself—is the guiding premise of the holiday genre mash-up “Silent Night.” But while that sentiment seems gung-ho, the actual execution is more than a little shaky. Note: Encanto 2021 Streaming

Writer/director Camille Griffin’s feature filmmaking debut is an ambitious but muddled mix of Christmas comedy and apocalyptic drama. Griffin has crafted a cautionary tale about climate change and tucked it inside a cozy, Richard Curtis-style British rom-com, starring a key figure of “Love Actually” in Keira Knightley. A giant, toxic cloud is sweeping across the planet, the result of irreparable, collective abuse and neglect. It’s expected to devour a motley assemblage of family and friends at a posh English country estate sometime after midnight, giving a whole new meaning to that ubiquitous Wham! earworm “Last Christmas.” Note: House of Gucci 2021 Streaming

While that sounds potentially intriguing, “Silent Night” doesn’t reach the fizzy heights of the familiar comedies that served as inspiration. It’s never all that amusing, and the characters feel like paper-thin versions of the kind of charmers we see in such films. At the same time, Griffin’s movie rarely achieves the suspenseful, unsettling vibe she’s aiming for once the story takes a dark turn around the halfway point. Several actors among the strong ensemble have standout moments—especially Roman Griffin Davis, the filmmaker’s son, who made such an impression as the young star of “Jojo Rabbit.” But on the whole, these are barely-there characters, so it’s difficult to care whether they live or die—or even whether they will choose to live or die.

The day begins with the usual combination of cheer and dread as couples and families gather for a Christmas feast at the home of Knightley’s Nell, her husband, Simon (Matthew Goode), and their three kids; besides Roman Griffin Davis’ Art, Hardy and Gilby Griffin Davis play twins Hardy and Thomas. (Griffin’s husband, Ben Davis, a veteran cinematographer whose work includes “Eternals,” “Doctor Strange,” “Three Billboards Outside Ebbing, Missouri” and several Matthew Vaughn films, also contributed behind the scenes. Vaughn is among the film’s producers, so the project feels like a family-and-friends affair all around.) The first sign that something is amiss amid the usual hustle and bustle is the fact that all of these tween-age children get to swear with wild abandon while they’re getting ready. Art cuts his finger while slicing carrots, bleeding all over the vegetables in an ominous sign. Note: Spider-Man : Far From Home 2021 Streaming

Then Nell’s preening sister, Sandra (Annabelle Wallis), arrives in a red-sequined, body-hugging stunner of a gown, complete with sparkly heels she bought with the money meant as college fund for prissy daughter Kitty (Davida McKenzie). Then again, everyone is overdressed, with Simon and the twins in tuxes, contributing to the vibe that something’s just a bit off. Also among the group are Sandra’s dull husband (Rufus Jones), as well as physician James (Sope Dirisu), the one who got away from when they all attended school together, and James’ much younger girlfriend, Sophie (Lily-Rose Depp). And there’s brash Bella (Lucy Punch) and her girlfriend, Alex (Kirby Howell-Baptiste), who watches and takes it all in as the night unravels.

Relatable humor comes from the awkwardness of these people trying to make small talk although they only see each other once a year, and these early scenes in which “Silent Night” plays like an agreeable, light farce—albeit with an undercurrent of menace—are the film’s strongest. The threat of impending doom keeps creeping into their forced joy, as in the gifts wrapped tidily in newspaper with headlines warning of global destruction. “Silent Night” ultimately becomes a crucible of who all these people really are as they relive old memories and rehash old regrets, but who they are turns out to be not all that interesting.

As the story progresses, Griffin swings between her initial comic instincts and a more dire tone in ways that feel ungainly. A melodramatic streak emerges, especially as the characters debate whether to take government-issued “Exit” pills to end it all peacefully or wait for the catastrophic effects of the poison to wash over them and see what happens. She reveals a gruesome discovery and smothers it with portentous music, but also shows the characters dancing around the living room to peppy songs like the theme from “Fame” (although, distractingly, it’s a cover of Irene Cara’s anthem).