Here’s the description of the novel the film is based on, written by Joe Hill. Horns opens in the US on Halloween.
Ignatius William Perrish wakes up bleary and confused after a night of drinking and “doing terrible things” to find he has grown horns. In addition to being horribly unsightly, these inflamed protuberances give Ig an equally ugly power–if he thinks hard enough, he can make people admit things (intimate, embarrassing, I-can’t-believe-you-just-said-that details). This bizarre affliction is of particular use to Ig, who is still grieving over the murder of his childhood sweetheart (a grisly act the entire town, including his family, believes he committed).