I, personally, do not like Sir Henry (although he is somewhat amusing), and there was far too much treacly and unconvincing romance in the telling of the tale, but the puzzle itself was fairly done.
There were too many conversations about important events started and never finished, with the actors just saying "forget it" and the others never pressing them to conclusions.
See p. 184 for the genesis of the book's title, in another uncompleted fragment.
There were also far too many important scenes elided.
I never understood why the instigator of the mystery even bring Merrivale into his scheme in the first place, which just increased his chances of getting found out.

Most mysteries are really best as short stories, IMO, except for Dorothy Sayers and Dick Francis. ( )

I'm sure most admirers of Carr/Dickson's writing would agree that his best work was done in the pre-war years. This book, first published in 1950, is no exception. However, even his lesser works are never less than enjoyable. Here the plot turns on the strange behaviour of the very respectable American philanthropist Frederick Manning, whose reverence for his late wife's memory seems to have taken a tumble when he becomes infatuated with a woman described variously as a floozie and a fan-dancer. What is more, there are rumours that his educational foundation is in financial trouble, and that Manning has behaved fraudulently. Matters come to a head when Manning pulls off a conjuring trick - in the presence of detective extraordinaire Sir Henry Merrivale (always known as H. M.) he dives into a swimming pool fully clothed and vanishes. The book's weakest point is the motivation for certain people's actions, which often doesn't make sense - but this problem is almost inescapable in this genre. ( )