This is the first Tommy and Tuppence novel, they are not my favourite Christie characters as I do find all the ‘old thing’ and ‘old bean’ stuff cliched, but on first release this book sold very well, so it may be that the book has not stood up to the passage of time. It certainly is very much a book of its time and the annoying over exuberance of the characters does reflect a certain post WWI attitude. One nice thing about this book is that Tommy and Tuppence are characterised as equal partners in their adventures, which for 1922 was very progressive.
This is a spoiler if you haven’t read the book, so stop here. But its interesting, especially if you follow Laura Thompson’s idea of looking for clues about Christie’s life in her texts, to note that in this book one of the characters pretends to have amnesia and sustains that deceit for a period of time. This book predates Agatha Christie’s breakdown, disappearance and only memory loss by some years, but it is an interesting parallel.