TOD: When I was in the fifth grade, I went through an intense Agatha Christie/Erle Stanley Gardner phase. Read dozens and dozens of their books and just couldn't get enough of them. I don't remember plots, but I do recall a few of the books that I liked and the characters, such as Tommy and Tuppence.
The Mysterious Affair at Styles
By the Pricking of My Thumbs
The Murder of Roger Akyroyd
Murder on the Orient Express
And Then There Were None
N or M?
Murder Is Easy
The Seven Dials Mystery
Films:
Evil Under the Sun
Murder on the Orient Express
Margaret Rutherford as Miss Marple in all of those movies