在美國密蘇里州的小鎮，公路旁的三塊大型告示牌，原本的舊廣告已經剝落殘破，但某天換上了新廣告，以大大的紅底黑字指控警長辦姦殺案不力。
廣告主是幾個月前失去女兒的Mildred（法蘭西絲麥多曼），被指名辦事不力的警長是Willoughby（伍迪哈里遜），警長忠心耿耿的副手Dixon（山姆洛克威爾）知道看板的事情後極為憤怒，想辦法惡整Mildred以及負責告示牌的Red（Caleb Landry Jones）。
故事起頭乍看很簡單，好像會演變為Mildred與惡警的對抗，但並非如此，它的主題遠比所謂善惡二元對抗大得多。《意外》不是三幕戲的傳統劇本，不是犯罪片，不是復仇片，它是關於人物的研究，三位主要角色都不是扁平人物，都有很多面向與層次需要觀察——他們的動機，他們的選擇，這些選擇又如何產生碰撞、影響，產生更多漣漪。
最重要的角色Mildred，生活一塊塊破碎瓦解。她的婚姻早已結束，與前夫的互動暗示著Mildred曾受家暴，女兒Angela生前與她處得並不好，女兒被姦殺後，Mildred更是被憤怒與自責吞噬，對兒子Robbie（在《海邊的曼徹斯特》飾演兒子的Lucas Hedges）沒有任何餘力關心或照顧。在一關又一關的挫折後，Mildred早已成了一隻鬥牛，隨時等著攻擊或羞辱對方。但這樣的好戰態度，令鎮民很難支持明明是受害者家屬的她，兒子的處境更是為難，不僅連帶受到他人的排擠，偌大的告示牌也天天提醒他這輩子最想忘掉的事情。
被她指責查了好幾個月都破不了案、讓全鎮女孩曝於險境的警長，也有無奈的理由。Angela的案子苦缺線索，沒有相符的DNA就是無法確認與逮捕嫌犯，而警長自己也面臨癌症威脅，來日無多，面對妻兒百味雜陳。Mildred放那三面告示牌點名警長，不僅於事無補，而且確實有欠厚道，也讓鎮民不諒解。
警長因為Mildred鑽傷牙醫手掌，偵詢Mildred，她賴皮表示這案子只有「他說，她說」各執一詞，辦不了她，還提到這跟Angela的案件一樣。她的戲謔嘲諷，其實也等於說明了她女兒的案件多麼難辦，把氣出在警長身上其實意義不大，只是在宣洩情緒，並讓自己覺得「我有在做些什麼」罷了。憤怒成了Mildred的面具，底下藏著悲痛與自責。憤怒讓她的人生破碎，卻也讓她感到解放。只要她不這樣憤怒，就會陷入悲傷的無底洞裡，如同她在告示牌下見到一頭鹿的那一刻。
Dixon乍看之下是個符合刻板印象的小鎮白人警察角色：似乎有點笨，但有十足的蠻力，愛打黑人出氣，很崇拜警長。但原來，他也在為脫離媽媽控制、真正長大而奮戰，並在某次受重傷送醫後，因為在醫院看見先前被他霸凌的人，對方的處境與態度，使Dixon對一切產生了新的想法。
每個人身上同時帶有善與惡，人的選擇則在整個善惡光譜上搖搖擺擺，有時下一刻就大移位。前述警長向Mildred問話的那幕，原本兩方對話屬於對抗狀態，但在某意外之事發生時，敵意頓時放了下來，觀眾可以感受到那一刻彼此的理解與同情，Mildred也變得溫暖許多。
而且「好人」這塊招牌，不一定必然與善惡有關，也不是每個人都扛得起的。怎麼樣算個「好人」？警長當然是個好男人，有幽默感，有家庭，有癌症。而Mildred，她不是個「好」女人，她的婚姻沒能維持住，又因為不甘心看女兒的案件成為死水，成天大張旗鼓，張牙舞爪，鎮民看著很不舒服。有這些背景的Mildred，在何種情形之下可以被大家當成好女人？很簡單：「安靜悲傷痛苦地接受女兒被姦殺、兇手逍遙法外的事實」。換句話說，就是，「有受害者的樣子」。Mildred選不了這條路，她若想扛「好人」招牌，比起其他人生相對順遂的人們，難度高很多。
不過，Mildred漸漸也發現，自己魯莽行事造成的傷害，再這樣下去她跟Dixon恐怕也沒什麼不同。甚至，Dixon也有了轉變，這兩人在類似的時間點開始領悟，要如何讓負面影響止在自己身上，甚至帶給他人正面影響？這可以是很小的動作，可以只是替之前揍過自己的人倒杯果汁。
有時我們需要用他人視角看事情，看看關於正義、關於原諒、關於給自己與他人第二次機會代表著什麼。《意外》有著濃濃的憤世嫉俗味道，卻也同時帶著希望。片尾兩名角色「到時再看著辦」的態度，暗示著他們還有更多時間與空間，可以學習如何用更好的方式面對這個世界。
編劇兼導演馬丁麥克唐納是劇作家出身，《殺手沒有假期》是他的導演長片處女作，我非常推薦。《意外》延續了前作的獨特黑色幽默，場景移到美國的虛構小鎮Ebbing，加入一些社會批判，穿插性別與種族歧視、暴力等等議題，尤其暴力在片中處處出現，但似乎也無法處理，只能說是一種正常能量釋放。我不確定導演選擇將背景設於密蘇里州，與幾年前發生白人警察槍殺黑人Michael Brown、並造成大規模抗議事件的Ferguson小鎮在同一個州，是否有關連，不過片中的各種暴力形式，在美國甚至全球各處，隨時都在發生，只能看人們是否有足夠能力，尋找更好的方式面對與處理了。
小花絮：《意外》靈感來自導演搭公車遊美國時，看到類似的告示牌杵在公路邊，等著廣告主放上想讓大家知道的訊息。
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經典對白：
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Mildred Hayes: So how's it all going in the nigger- torturing business, Dixon?
Dixon: It's 'Persons of color'-torturing business, these days, if you want to know. And I didn't torture nobody.
***
Mildred Hayes: Y'know what I was thinking about today? I was thinking 'bout those street gangs they had down in Los Angeles, the Crips and the Bloods? I was thinking about that buncha new laws they came up with, in the 1980's I think it was, to combat those street-gangs, those Crips and those Bloods. And, if I remember rightly, the gist of what those new laws were saying was if you join one of these gangs, and you're running with 'em, and down the block one night, unbeknownst to you, one of your fellow Crips, or your fellow Bloods, shoot up a place, or stab a guy, well then, even though you didn't know nothing about it, even though you may've just been standing on a streetcorner minding your own business, what these new laws said was you are still culpable. You are still culpable, by the very act of joining those Crips, or those Bloods, in the first place. Which got me thinking, Father, that whole type of situation is kinda like your Church boys, ain't it? You've got your colors, you've got your clubhouse, you're, for want of a better word, a gang. And if you're upstairs smoking a pipe and reading a bible while one of your fellow gang members is downstairs fucking an altar boy then,Father, just like the Crips, and just like the Bloods,you're culpable. Cos you joined the gang, man. And I don't care if you never did shit or never saw shit or never heard shit. You joined the gang. You're culpable. And when a person is culpable to altar-boy-fucking, or anykinda-boy-fucking, I know you guys didn't really narrow it down, then they kinda forfeit the right to come into my house and say anything about me, or my life, or my daughter, or my billboards. So, why don't you just finish your tea there, Father, and get the fuck outta my kitchen.
***
Willoughby: I'd do anything to catch the guy who did it, Mrs. Hayes, but when the DNA don't match no one who's ever been arrested, and when the DNA don't match any other crime nationwide, and there wasn't a single eyewitness from the time she left your house to the time we found her, well... right now there ain't too much more we could do.
Mildred Hayes: You could pull blood from every man and boy in this town over the age of 8.
Willoughby: There's civil rights laws prevents that, Mrs. Hayes, and what if he was just passing through town?
Mildred Hayes: Pull blood from every man in the country.
Willoughby: And what if he was just passing through the country?
Mildred Hayes: If it was me, I'd start up a database, every male baby was born, stick 'em on it, and as soon as he done something wrong, cross reference it, make 100% certain it was a correct match, then kill him.
Willoughby: Yeah well, there's definitely civil rights laws that prevents that.
***
Mildred Hayes: My daughter Angela was murdered 7 months ago, it seems to me the police department is too busy torturing black folk to solve actual crimes.
***
在美國密蘇里州的小鎮，公路旁的三塊大型告示牌，原本的舊廣告已經剝落殘破，但某天換上了新廣告，以大大的紅底黑字指控警長辦姦殺案不力。
廣告主是幾個月前失去女兒的Mildred（法蘭西絲麥多曼），被指名辦事不力的警長是Willoughby（伍迪哈里遜），警長忠心耿耿的副手Dixon（山姆洛克威爾）知道看板的事情後極為憤怒，想辦法惡整Mildred以及負責告示牌的Red（Caleb Landry Jones）。