Starring Christopher Plummer. Rated 14A

“I’m so fucked-up,” says Vera Farmiga’s persistently dishevelled Laura Jaconi, “I can’t even tell my therapist how fucked-up I am.” It’s one of the funniest, most self-aware moments in a tale that is otherwise clueless and lacking in laughs.

A road movie with a fixed destination and no working GPS, Boundaries appears to have assembled a great cast around an overly familiar idea and then left the script too late. That’s weird, because this is the fourth feature for writer-director Shana Feste, best-known for her goopy Gwyneth Paltrow vehicle Country Strong. (Never heard of Feste’s 2014 remake of Endless Love? You’re not alone.)

Here’s the concept: middle-aged Laura has abandonment issues, thanks to endless disappointments from her shiftless father, Jack (Christopher Plummer), who’s getting kicked out of his retirement home for growing pot. Her sad past has caused Laura to fill her home with mangy stray cats and dogs. And she’s far too close to her geeky teenage son, Henry (A Monster Calls’s Scottish-born Lewis MacDougall). He’s always in trouble for drawing obscene naked portraits of teachers and his mother’s fleeting boyfriends. Are you chortling yet?

When absent Dad begs Laura for help, the best she can offer is getting him to her more tolerant sister, JoJo (The Daily Show’s Kristen Schaal), in L.A. Jack says he can’t fly, so Laura reluctantly agrees to drive him in his ancient Rolls-Royce, with Henry in tow. She takes time off from a job that is never really explained to go on a mission that makes no sense; she knows, even if we don’t, that JoJo lives in a 400-square-foot rented apartment, while Laura has a huge, free-standing house in Seattle, presumably paid for by that mystery job.

She needs to make the trip as quick as possible, so of course she takes Highway 101, with a trunk filled with pot he sells along the way without her ever figuring it out. (Guess I’ve been picking the wrong rest stops for my old-rock-music montages.) The Canadian-enabled film makes adequate, if dimly lit, use of B.C. locations subbing for the American west coast going south. Granville Island stands in for Sausalito, where her deadbeat ex-husband (Bobby Cannavale) lives on a houseboat. It’s hard to say what’s more poorly written, their disjointed family reunion (“What’s your problem, kid?”) or the pointless visit with Peter Fonda, as a rich guy who buys the rest of Jack’s stash.

Christopher Lloyd fares better as a fellow old-timer off the grid. But none of these encounters are used to deepen Jack’s back story or change Laura’s perceptions of him. Instead, it’s left entirely to the actors to oversell their thin material, and the effort is all too visible. Maybe they should have had Plummer play all the parts.