I have to be honest with you: there are very few circumstances under which you should see Dirty Grandpa. If a psychotic villain is making you fight for your life with a series of desperate, Saw-like challenges and one of them involves making it all the way through this movie, you should watch it. If you can’t make it another day without investigating the intimate parts of Zac Efron on which this movie is so reliant, I respect your thirst; you should watch it, I guess, but you’ve been warned. Everyone else should steer clear. The 90 minutes you spend watching Robert De Niro prowl Florida for horny college girls the day after his beloved wife’s death can’t be recovered.

I don’t meet either of the conditions above, but I went to see Dirty Grandpa last night nonetheless. You can chalk it up to one part morbid curiosity and one part genuine investment in Efron’s cinematic career. You wouldn’t know it from a look at his IMDb page, but he remains one of the most beguiling young actors around. He’s also arriving at a career inflection point: Dirty Grandpa is Efron’s first movie after the historic commercial failure of We Are Your Friends, the unfairly maligned EDM dramedy in which he played an ascendant San Fernando Valley DJ. It’s also being released just after the tenth anniversary of High School Musical, the Disney Channel phenomenon that enabled Efron’s minor stardom in the first place.

High School Musical and Dirty Grandpa end up having more in common than you’d expect. In both movies, Efron plays a straight-laced, subservient hunk whose true passion is being compromised by paternal pressure and societal expectations. He’s ultimately liberated from his staid life, and he gets to sing and dance along the way. The fundamental parts of his appeal as an actor haven’t changed in the decade separating the two movies, either. He’s charming but harmless; there are several points in Dirty Grandpa at which you’re supposed to feel like Efron might actually snap at De Niro, but he just can’t get there. (You’re left begging for the punch to the jaw you know can’t happen.)

He’s achieved a surprising sort of physical presence through sheer will and protein shakes, but he’s too anatomically precise — cartoonish, even — to feel sexy. The scenes in which Efron performs a nearly-naked version of the Macarena and sings Céline Dion’s "Because You Loved Me" at a karaoke bar are the rays of light that creep into Dirty Grandpa’s subterranean torture chamber, but you don’t want to take him home. You’re just happy he’s having fun. The most exciting thing about him is his eagerness to play the fool, the whipping boy, and the sponge. You can imagine him giddy over the chance to work with an acting legend, and there’s still a tiny gleam in his eye as he’s subjected to De Niro’s misogynistic, homophobic, relentlessly horny tirades: "I’m being abused by Robert De Niro!" He wants to push himself, but he can’t figure out how to do so without trading on his body’s appeal.

All of Efron’s adult movies leave you thinking about the death of something. Neighbors (which remains his best movie by a wide margin) and We Are Your Friends approach the end of his youth from two different angles; the latter is more optimistic, but he’s still leaving a version of his life behind. Dirty Grandpa is less subtle — the entire movie revolves around De Niro’s quest to get laid one last time before he croaks — and much less impactful. Even his body demands you reflect on mortality: you look at him and think, "my chances of ever looking like that are in the rear-view mirror and fading fast."

I spent the last half-hour of Dirty Grandpa trying to chart a path forward for Efron that’s reliant on something other than his arms and abs. He has definite limits as an intellectual presence — and Dirty Grandpa tests them by asking us to believe he’s a rising corporate lawyer — but he can do something with creative proficiency. When he gets the chance to handle a camera in this movie, you can feel a spark that’s dead everywhere else.

It’s the same spark that flies when he’s singing and dancing; it’s the same spark that lit up parts of We Are Your Friends, the ones where Efron sat behind a mixing console and tried to stitch something together. You believe in him wanting to work it out. His next few movies include a Neighbors sequel, a wedding comedy, and a Baywatch big screen reboot with Dwayne Johnson. It's hard to feel hopeful given their premises, but I want Efron to have the chance to show off something other than a muscle.