Cousins Scarlett Parker and Vivian Tremont’s fashionable London hat shop, Mim’s Whims, is visited by a new customer bearing an old hat box. Ariana Jackson is getting married and wants to restore her mother’s bridal hat and veil for the occasion. The elegant item was made by Scarlett and Vivian’s grandmother over thirty years ago, so Viv is delighted to take the job. When Scarlett goes to Ariana's office to consult about the restoration cost, she finds her outside, standing over her boss’s dead body. Though Ariana claims to know nothing about his demise, the investigation unveils a motive for murder. Now, with the bride-to-be in custody and the wedding on hold, Scarlett and Viv must find the real killer before Ariana's future is boxed up for good.

史嘉蕾和薇薇安這對表姊妹在倫敦所經營的 Mim’s Whims 精品帽子店來了一位新訪客，手裡提著一個老舊的帽盒。這名訪客名為亞利安娜，即將結婚的她想要將媽媽以前結婚時所佩戴的帽子和面紗重新整理，等她結婚時再拿出來穿戴，而這優雅的配件是史嘉蕾和薇薇安的祖母三十年前左右所製作的，所以薇薇安很高興能接下這個工作。當史嘉蕾到亞利安娜的辦公室商詢問維修費用時，她發現亞利安娜的老闆竟然陳屍在外面，亞利安娜就站在屍體旁邊。雖然亞利安娜聲稱老闆的死她一點也不知情，但調查結果不排除有謀殺的嫌疑。現在，準新娘遭到羈押，婚禮遙遙無期，史嘉蕾和薇薇安必須盡快找到真正的兇手，否則亞利安娜的未來將如同舊帽子般永遠被塵封在盒子裡。