Un, deux, trois...

Reviewers widely praise this novel for its exciting and captivating plot, describing it as a great story brimming with twists, turns, and clever red herrings that keep readers guessing until the very end. Many appreciated the intricate and complex nature of the mystery, often highlighting Agatha Christie's ingenious writing and the unique structural device of incorporating a nursery rhyme. A significant positive noted is the portrayal of Hercule Poirot, who appears more human and vulnerable, particularly in his fear of the dentist, and exhibits a less self-important demeanor with glimpses of moral dilemma, making him a more relatable and three-dimensional character. The case is often cited as one of Poirot's most complex, with well-crafted details and a satisfying, often unexpected, resolution. Some also enjoyed the elements of spy thriller and political intrigue woven into the narrative.

Despite the positive reception, some reviewers found the story confusing, overly complicated, or convoluted, particularly towards the ending, with revelations that felt contrived or improbable. A recurring criticism concerns the characters, who some described as pale, lacking depth, or too numerous, making them difficult to distinguish or connect with. For seasoned Christie readers, the book sometimes fell short of her "crème de la crème," being deemed less memorable or one of Poirot's weaker cases. The motive for the crime was occasionally perceived as ludicrous or unconvincing, and some did not enjoy the political or espionage themes. Additionally, the central investigation was described as slow by some, and a few felt the ending was impossible to predict, detracting from the "fair play" aspect of the mystery. The clever nursery rhyme structure, while appreciated by many, also made the narrative feel stiff to a few.

Overall, this book is considered a solid and enjoyable read, highly recommended for existing fans of Agatha Christie and Hercule Poirot who appreciate her classic mystery elements and the nuanced character development of the detective. It also holds appeal for newcomers looking for a complex, twist-filled mystery that showcases Christie's talent for intricate plotting. Readers who enjoy a less predictable ending, a more human Poirot, and don't mind a slower pace in the middle will likely find this a rewarding experience. It serves as a good companion for those seeking a well-written, engaging mystery, even if it might not rank among the author's absolute best for some.