I'm torn on this story, really.
On the plus side, it's nice for variety, with a more supernatural atmosphere (although there isn't actually any supernatural agency involved), and breaks up the more typically crime-based stories nicely. It's also pretty clever, and enjoyable for that.
On the other hand, there are some things that just don't make sense. Like if the blood stain that she saw was really actually there... why didn't she see anything when she went across the road to look, or why didn't the Captain see it? Not to mention there is a bit of coincidence what with her just happening to be right on the spot two years running when this guy pulls his little scam.
Anyhow, Joyce does seem to have a bit of the temperament usually attributed to artists, what with her dramatic "I KNEW the captain wouldn't see what I saw! I just knew it!" bit, but otherwise she seems fairly sensible and intelligent.
Miss Marple hovers between "well-done" and "overdone" in the book in general, I think, but I do like the ending image of the sweet little old lady hoping that the poor young folk never realize how really wicked the world is.