Ingenious plot based on and incorporating the old nursery rhyme "Sing a song of sixpence". I wonder who first originated the idea of serial killings as a sort of game? Whoever it was, I'm blaming them for all the unsatisfactory plot resolutions and silly motives for murder that result. This is unfortunately one of them. Luckily in this case, it's saved by Christie's brood of highly suspicious characters and funny personalities.