“Gimme Shelter” is a simplistic, faintly emotional account of a pregnant teen’s desperate search for help, support and compassion with the huge decision she faces. It’s simplistic because the script discounts debate over that decision and glosses over the messy details of the path she chooses. But it’s emotional because we, and plainly some of the characters, know those messy details, even if other characters do not.

Agnes (Vanessa Hudgens) is 16 and poor, the daughter of a drug addict (Rosario Dawson) who had her too young. Agnes, who decides she wants to be called “Apple,” is all piercings, ill-fitting dirty clothes and tattoos. And if she needs a case study in how life can go wrong by having a baby at that tender age, she can look at Mom — a raging, staggering horror in her early 30s.

But Apple, with no more warning than an “I’m OUT,” runs away. With just a little cash and a crumpled envelope with an address on it, she sets out in search of the father she’s never met.

She runs into misadventures — threats from a pimp, a car crash, an arrest. Her affluent, suburban dad (Brendan Fraser) has two kids, a gorgeous French wife (Stephanie Szostak) and enough guilt to take her in. But the wife won’t stand for it.

Apple’s mother, wanting that extra welfare check, is tracking her down. As street-savvy as this sullen, standoffish girl is, she’s in way over her head.

“Gimme Shelter” has many of the hallmarks of a faith-based film, the ways it lays out Apple’s dilemma, the grim details of her life that Hudgens milks for all they’re worth, the people of faith who offer her hope and her resistance to their ministry.

A priest (James Earl Jones) and a shelter run by the understanding but no-nonsense Kathy (Ann Dowd of “Side Effects” and “Compliance”) offer Apple sanctuary. Does she have the good sense to take it, or will she bring the problems of her world crashing into theirs?

Writer/director Ron Krauss embraces the grit but fails to find much that surprises here. He attracted a good cast, and Hudgens, hell-bent on leaving her Disney “High School Musical” image behind, dives into the street language and angry, downcast look of a defiant girl who doesn’t know how little she knows about how bad things are and how much worse they could get. With this film, following “Sucker Punch,” “Spring Breakers” and “The Frozen Ground” (she played a young hooker in that one), Hudgens has had a lot of practice dressing down and exploring the ugly side of life.