在这部蒙面女人悬疑/犯罪片中,周五，一个戴黑色面纱的神秘女郎约见波罗，声称有一个名叫莱应的顿的恶棍，在得知她即将与公爵结婚的消息后，手持她16岁时写的一封“轻率而愚蠢”的情书向她勒索2万英镑。当晚，波罗与黑斯廷斯约见了令厌恶的莱应顺，双方不欢而散，这样一来，就让波罗有了去实现其犯罪抱负的借口。
第二天夜里，波罗与黑斯廷斯乔装打扮，带着手电、小刀等作案工具，爬进莱应顿的公寓。爬高伏低，大肆搜索装有那封致命情书的“字迷盒子”。警方迅速赶到，将波罗一举擒下并关入铁牢。
在警局里，波罗意外得知，莱应顿早在周二就已被人谋杀……
“当波罗决定要当一名世界上最伟大的侦探时，这个世界失去了一个技艺高超的盗贼。”
Poirot despairs at the lack of crime - and work - concluding that he, Hercule Poirot, has scared off the criminal classes. His mood brightens when Lady Millicent Castle-Vaughn - the veiled Lady of the title - asks him to recover from her blackmailer some indiscreet letters written in her youth. Unable to convince the man to reduce the amount asked for, Poirot decides to take matters into his own hands and steal them. As Poirot and Hastings learn however, not all is as it seems, starting with Lady Millicent.
