While exploring a Mississippi River island, Arkansas boys Ellis (Tye Sheridan) and Neckbone (Jacob Lofland) encounter Mud (Matthew McConaughey), a fugitive who needs their help. Though Mud killed a man in Texas and has bounty hunters on his trail, he is most concerned about reuniting with Juniper (Reese Witherspoon), the love of his life. Ellis, who is suffering the pangs of his first crush, agrees to help Mud. He and Neckbone do all they can to protect Mud and help him reunite with Juniper.