An Autistic young “Star Trek” fanatic expands her horizons on her first-ever road trip on her own in “Please Stand By,” a picture whose picaresque premise holds more promise that its star or director deliver.

The heroine of the piece works at a Cinnabon and has written a script for “Star Trek” screenplay contest. She skips out of a group home in the San Francisco Bay area, with her Trek-attired chihuahua in tow, to deliver the tome, in person, to Paramount Pictures in Hollywood. You’d think there’d be some light moments in that — misadventures on the lam, getting robbed, surviving a bus wreck, confronting snotty studio functionaries.

But no. This is a “serious” road comedy about autism. Or at least it is in the hands of director Ben Lewin (“The Sessions,” “Paperback Romance”) and his star Dakota Fanning. The most ardent supporters of either would have to confess that “light” isn’t really in their repertoire. They conspire to throw the whole tone of the picture off, with only comic Patton Oswalt’s arrival in the third act providing so much as a smile.

And, well, the dog’s cute.

Fanning is Wendy, who has to treat every potential human interaction as a project, requiring her full attention. She must say “Welcome to Cinnabon. Would you LIKE a Cinnabon?” differently every time she tosses it at a potential customer.

Her therapist and coach at the halfway house (Toni Collette) has worked long and hard to get Wendy this far out into the world, working, practicing interpersonal skills.

“Can we try three seconds of eye contact?”

Wendy’s therapist is conveniently named “Scottie.” Because Wendy is deep into “Star Trek.” She clatters away at her epic script for the franchise, with plans to get it into the mail and into a contest Paramount is throwing for ardent fans of the series. We hear Wendy narrate scenes, and sometimes see space-suited characters wander the desert in a spot-on allegory for how someone “on the spectrum” might view the hostile world

Wendy hopes to win the contest and see her story produced. But her most fervent hope is that she’ll win, “be able to buy mom’s house back” and come off as “normal” enough for sister Audrey (Alice Eve) to bring her home so that she can start being an aunt to Audrey’s new baby. The occasional violent fit, which Scottie talks her out of with the calming phrase “Please stand by,” suggests that won’t happen.

Events conspire to make Wendy miss her mailing deadline for the contest. There’s nothing for it but to make the trip to LA to hand-deliver it. Wendy rides the bus to work. There’s a bus to LA. Easy peasy, right?

Of course not.

And the fact that she didn’t tell anybody where she was going sends one and all into a panic.

We can trust Lewin, a rare disabled director, to treat any disability with the utmost sensitivity on screen, and he does. What we can’t trust him or the humorless Fanning to do is to make this fish-out-of-water road picture funny, to make Wendy anybody we want to spend time with or any of Wendy’s encounters (Marla Gibbs plays a senior citizen who “rescues” her) amusing or interesting.

Until, that is, Oswalt arrives.

More could have been made out of the “Star Trek” opus, comic parallels with Wendy’s own dilemma (the dog gets her kicked off the bus). A life this sheltered experiencing the big wide world for the first time can be “Rainman” fraught and funny. Not here.

Fanning makes Wendy a compulsive knitter, and is does the whole never-make-eye-contact thing with commitment and skill, but utterly without warmth. That’s a knock that’s dogged her throughout her career, so even the character’s suitability to her skill-set that works against her here.

Her co-stars have little to play. The trip itself is a fairly unsurprising and colorless affair, with Wendy finding allies and obstacles in the usual places.

Thus does the generally lifeless “Please Stand By” only discover signs of life when our heroine gets to LA, where everybody wants to be “in the business,” where every mailroom wannabe on a studio payroll is on a power trip and every police force has its share of native Klingon speakers.

MPAA Rating: PG-13 for brief strong language

Cast: Dakota Fanning, Toni Collette, Alice Eve, Patton Oswalt

Credits:Directed by Ben Lewin, script by Michael Golamco. A Magnolia release.

Running time: 1:33