In Logan Marshall-Green’s “Adopt a Highway,” Ethan Hawke offers a sensitive performance as a severely introverted ex-con who learns to reconnect with the world, at least to some extent. But while it has affecting moments, as a whole the film is so insubstantial as to virtually evaporate as you watch it.

It opens as Russell Pine is collecting his belongings in preparation for leaving a California prison after serving twenty years for marijuana possession. His sentence was the result of the state’s three-strikes law, which mandated stiff punishment for even minor multiple offenses. Among his possessions is a bunch of old newspaper clippings, one showing him as a teen in connection with an “adopt a highway” program.

Russell is rather lost in the real world, but the government provides him with a small apartment while he is on probation, along with a job at a fast-food restaurant run by a woman named Becca (Diane Gaeta). He uses a computer to read the obituary for his father, who died some years before in Wyoming, but otherwise seems to be just ambling about without much purpose.

That changes when he finds a baby in the dumpster behind the restaurant, with a note saying the child’s name is Ella (Everly and Savannah Sucher). He takes the infant back to his dingy place and attempts to take care of her—getting some advice from a clerk (Loni Love) in a grocery store—but panics when he learns that he could be charged with kidnapping and takes the child to the police. Afraid of their questions, he quickly leaves town by bus, and along the way to Wyoming makes friends with a gregarious blonde (Elaine Hendrix).

Returned to Casper, Russell visits his father’s grave and eventually his banker, who gives him the key to a safety deposit box that contains not only a touching letter from dad encouraging him to interact with the world but an inheritance as well, which he will use both to set up a trust for Ella and to embark on a journey to see the country. Finis.

This is a fairly thin reed on which to hang an entire feature film, even one barely running eighty minutes, especially since the script leaves so many questions about Russell’s past and personality unaddressed—along with the legal issues that presumably would have resulted from his violating the conditions of his parole.

What it has going for it is Hawke, who brings sweetness and muted sadness to the lead character, who may be underwritten but, when played by an actor of this quality, can’t help but touch the heart. A few of the supporting performers, like Love and Hendrix, add some breadth to what’s basically a very narrow slice of life, and the technical credits, from the lensing of Pepe Avila del Pino down, are adequate.

“Adopt a Highway” is no indie gem, but Hawke’s performance at least makes it watchable.

And you can say one other thing about it: this is certainly one of the more unlikely projects to be associated with the Blumhouse factory, which specializes in modestly-budgeted horror movies.