The central character in Christopher Cantwell ’s small-scale thriller, “The Parts You Lose,” is a lonely 10-year-old named Wesley. As played by the deaf British actor Danny Murphy , Wesley is watchful and careful in his movements, as if hoping that the school bully won’t notice him. He always does.

At home with his mother (a warm Mary Elizabeth Winstead ) and his little sister, Wesley is happier — at least until his gruff father, Ronnie ( Scoot McNairy ), returns home after an unspecified absence. Depressed and in denial about the extent of his son’s deafness , Ronnie refuses to learn sign language or help the boy to communicate. Despite the brevity of these scenes, the actors establish the family’s strained dynamic so adroitly that when the boy finds a wounded fugitive ( Aaron Paul ) and decides to nurse him back to health, we don’t need to be told why.