The Mysterious Edge of the Heroic World

Blurb

The Mysterious Edge of the Heroic World is a middle-age or young-adult novel by E.L. Konigsburg. It is a kind of detective story and some reviews present it as mystery fiction.
Amedeo Kaplan is both new boy and rich boy in the sixth grade. He longs to discover something "no one" yet knows. He volunteers to help liquidate the portable property of an elderly woman who once sang opera in Europe and finds himself learning more about degenerate art and the German occupation of the Netherlands.
The Mysterious Edge is a kind of sequel to The Outcasts of 19 Schuyler Place. Margaret Kane's two executive allies in The Outcasts are Amedeo Kaplan's godfather and mother here, about fifteen years later, and Vanderwaal family history is one aspect of The Mysterious Edge.