‘Flower’ is a coming-of-age revenge tale aiming for dark, but missing the comedy

When we meet Erica, the 17-year-old girl at the center of “Flower,” she’s in the process of blackmailing a police officer — performing oral sex on him in his squad car while her friends secretly film the encounter from outside. He isn’t the first to fall for her extortion. The little group has been making money this way all over town.

It’s for a good cause: Erica (Zoey Deutch) hopes to save enough to bail her dad out of jail.

“Flower” wastes no time — although it sure wastes plenty of energy — letting us know that its protagonist (and, by extension, the movie) revels in edginess. Just to put a cherry on top of things, we’re soon shown a peek inside Erica’s notebook, where she has a gallery of hand-drawn penis portraits, labeled by their owners’ names. She also punches a classmate in the face.

We’ve seen high-schoolers behaving badly before, sometimes to brilliant and entertaining effect. (Think “Heathers,” “Mean Girls” and the recent “Thoroughbreds.”) But “Flower” can’t quite nail the necessary tone, aiming for dark, but missing the comedy.

The plot gets going in earnest when Luke, the 18-year-old son of Erica’s future stepfather, moves in with Erica’s family, fresh out of rehab. “I thought junkies were supposed to be skinny,” Erica tells her mother (Kathryn Hahn) when she first sees her portly new housemate. Erica eventually warms to Luke (Joey Morgan) when she learns that he once accused a male teacher of fondling him and is still reeling after running into the man (Adam Scott).

In short order, Erica hatches a plan, along with Luke and her two extortionist friends (Dylan Gelula and Maya Eshet), to exact revenge. “Shaking down a child molester is our moral obligation,” she says.

It’s a mission that’s destined to go too far.

What sells the movie are the performances, especially Deutch’s. The 23-year-old daughter of actor Lea Thompson and director Howard Deutch, the performer has an unforced charisma and is a delight to watch — even when the script isn’t doing her any favors. She and Hahn, in the role of Erica’s laissez-faire single mother, play especially well off each other.

But Deutch’s character undergoes some bizarre changes of heart: If at first Erica is overly broad — a paint-by-numbers wild child — by the end of the film, she’s beyond comprehension, a teenage girl written by grown-ups who don’t understand teenage girls. Initially cryptic, Luke, by contrast, is at least understandable, once he has laid out his ulterior motives. Morgan emerges as the movie’s breakout star.

As “Flower” reaches its climax, director Max Winkler, who co-wrote the script with Matt Spicer and Alex McAuley, switches gears on his enigmatic main character, dropping the negative portrait for a heartwarming one. It’s a strange, but hardly bold, choice. Turns out, the only thing more confounding than Erica is the movie’s attempt at happy-ever-after.