The crossword solution for the term SEAN OF 'MYSTIC RIVER' is PENN, which is a four letter word. Sean of 'Mystic River' is a character from the 2003 American drama film of the same name, directed by Clint Eastwood and starring Sean Penn in the lead role. Penn plays the role of Sean Devine, a former police detective who is investigating a murder in his hometown of Mystic River, Massachusetts.