As The Mysterious Affair at Styles comes to a close, Hastings demands that Poirot explain the logic behind his mysterious actions throughout the novel—especially his decision to keep Hastings in the dark regarding the identity of the culprit. While Poirot indulges this request, he takes some time to examine the antagonists’ central construction of the mystery. In doing so, Poirot uses verbal irony to present Inglethorp’s line of thinking as he developed his plan:
Because, mon ami, it is the law of your country that a man once acquitted can never be tried again for the same offence. Aha! but it was clever—his idea! Assuredly, he is a man of method. See here, he knew that in his position he was bound to be suspected, so he conceived the exceedingly clever idea of preparing a lot of manufactured evidence against himself. He wished to be suspected. He wished to be arrested. He would then produce his irreproachable alibi—and, hey presto, he was safe for life!
As Poirot explains how Inglethorp worked out his plan to avoid discovery in the passage above, he expresses a degree of admiration for the level of method and detail the antagonist put into his alibi. However, the very fact that Poirot is able to figure out what happened proves that Inglethorp's planning was not thorough enough to avoid detection. When Poirot says, "[...] hey presto, he was safe for life!", he is using verbal irony—after all, Inglethorp is not, in fact, "safe for life." The flimsy staying power of Inglethorp’s supposedly “irreproachable” alibi makes it clear that Poirot is speaking facetiously, ultimately using irony to emphasize Inglethorp's misguided belief that he would be able to pull off this plan.
