VENICE (Reuters) – A lonely teenager takes to the road with an aging race horse he has saved from slaughter, in a movie that premiered in Venice on Friday that, according to its star, is about a simple but rare human quality: kindness.

Charlie Plummer plays Charley in “Lean on Pete”, a 15-year-old whose mother left when he was young and whose father’s drinking and womanizing leads to a heap of trouble.

Taking the horse he has befriended during a summer job at a local racetrack, Charley, penniless and homeless, sets off through the desert hoping to find a place to call home with a relative he hasn’t seen in years.

Plummer, an 18-year-old taking the biggest film role of his career, told Reuters at the Venice Film Festival the movie challenges the viewer to feel more compassion for people who are facing difficulties in life, including the homeless.

“We need more kindness and compassion in the world and we need to be able to realize that everybody is struggling and understand that we are more similar than we are different and feel that,” he said.

Directed by British filmmaker Andrew Haigh, “Lean on Pete” is based on the novel by Willy Vlauti.

Haigh, who won plaudits for the 2011 gay romance “Weekend” said “Lean on Pete” is something of a pre-coming-of-age story

“It’s almost like Charley hasn‘t got time to even begin to understand really who he is because he is always moving and fighting and trying to get some kind of home,” Haigh said.

“It was almost like that the coming of age story will be the next chapter in that story, oddly. That’s what kind of really appealed to me about it.”

The movie is one of 21 U.S. and international movies competing for the Golden Lion that will be awarded on Sept. 9.